{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Selecting Rows\n",
    "\n",
    "- [Download the lecture notes](https://philchodrow.github.io/PIC16A/content/pd/pd_2.ipynb). \n",
    "\n",
    "In the last lecture, we saw how to extract specific columns from a data frame. In many cases, we also need to extract specific rows. This operation is often called \"filtering\" -- we are filtering out the rows that we don't want, leaving the ones that we do. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import pandas as pd\n",
    "import numpy as np"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 48,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Species</th>\n",
       "      <th>Region</th>\n",
       "      <th>Island</th>\n",
       "      <th>Culmen Length (mm)</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>0</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>1</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.5</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>40.3</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>3</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>4</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>36.7</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "                               Species  Region     Island  Culmen Length (mm)\n",
       "0  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.1\n",
       "1  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.5\n",
       "2  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                40.3\n",
       "3  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                 NaN\n",
       "4  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                36.7"
      ]
     },
     "execution_count": 48,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# you'll need to run the first block in pd_2.ipynb \n",
    "# to download the data if you have not already done so\n",
    "\n",
    "penguins = pd.read_csv(\"palmer_penguins.csv\")\n",
    "# just the first five rows and selected columns\n",
    "penguins = penguins[[\"Species\", \"Region\", \"Island\", \"Culmen Length (mm)\"]]\n",
    "penguins.head()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The simplest way to select rows of data is by explicitly naming the value(s) of the index for the rows you want. Remember that the index is the set of bold numbers at the far left. To do this, you should use the `df.loc` attribute of the data frame, like this: "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 49,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Species</th>\n",
       "      <th>Region</th>\n",
       "      <th>Island</th>\n",
       "      <th>Culmen Length (mm)</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>1</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.5</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>40.3</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>3</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "                               Species  Region     Island  Culmen Length (mm)\n",
       "1  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.5\n",
       "2  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                40.3\n",
       "3  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                 NaN"
      ]
     },
     "execution_count": 49,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "penguins.loc[1:3] # rows with index values 1 through 3"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 50,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Species</th>\n",
       "      <th>Region</th>\n",
       "      <th>Island</th>\n",
       "      <th>Culmen Length (mm)</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>1</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.5</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>4</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>36.7</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>0</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.1</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "                               Species  Region     Island  Culmen Length (mm)\n",
       "1  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.5\n",
       "4  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                36.7\n",
       "0  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.1"
      ]
     },
     "execution_count": 50,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# passing an explicit list can change the order of the rows. \n",
    "s = penguins.loc[[1, 4, 0]]\n",
    "s"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 51,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "Species               Adelie Penguin (Pygoscelis adeliae)\n",
       "Region                                             Anvers\n",
       "Island                                          Torgersen\n",
       "Culmen Length (mm)                                   36.7\n",
       "Name: 4, dtype: object"
      ]
     },
     "execution_count": 51,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# note that this works, even though s does not have a 4th row, \n",
    "# because s does have an index with value 4\n",
    "s.loc[4]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 52,
   "metadata": {},
   "outputs": [
    {
     "ename": "KeyError",
     "evalue": "2",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mKeyError\u001b[0m                                  Traceback (most recent call last)",
      "\u001b[0;32m/opt/anaconda3/lib/python3.8/site-packages/pandas/core/indexes/base.py\u001b[0m in \u001b[0;36mget_loc\u001b[0;34m(self, key, method, tolerance)\u001b[0m\n\u001b[1;32m   2645\u001b[0m             \u001b[0;32mtry\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 2646\u001b[0;31m                 \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_engine\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mget_loc\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mkey\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m   2647\u001b[0m             \u001b[0;32mexcept\u001b[0m \u001b[0mKeyError\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32mpandas/_libs/index.pyx\u001b[0m in \u001b[0;36mpandas._libs.index.IndexEngine.get_loc\u001b[0;34m()\u001b[0m\n",
      "\u001b[0;32mpandas/_libs/index.pyx\u001b[0m in \u001b[0;36mpandas._libs.index.IndexEngine.get_loc\u001b[0;34m()\u001b[0m\n",
      "\u001b[0;32mpandas/_libs/hashtable_class_helper.pxi\u001b[0m in \u001b[0;36mpandas._libs.hashtable.Int64HashTable.get_item\u001b[0;34m()\u001b[0m\n",
      "\u001b[0;32mpandas/_libs/hashtable_class_helper.pxi\u001b[0m in \u001b[0;36mpandas._libs.hashtable.Int64HashTable.get_item\u001b[0;34m()\u001b[0m\n",
      "\u001b[0;31mKeyError\u001b[0m: 2",
      "\nDuring handling of the above exception, another exception occurred:\n",
      "\u001b[0;31mKeyError\u001b[0m                                  Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-52-1d3ba2e47d68>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;31m# on the other hand, this doesn't work\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m \u001b[0ms\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mloc\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m2\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m/opt/anaconda3/lib/python3.8/site-packages/pandas/core/indexing.py\u001b[0m in \u001b[0;36m__getitem__\u001b[0;34m(self, key)\u001b[0m\n\u001b[1;32m   1766\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1767\u001b[0m             \u001b[0mmaybe_callable\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mcom\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mapply_if_callable\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mkey\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mobj\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 1768\u001b[0;31m             \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_getitem_axis\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmaybe_callable\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0maxis\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0maxis\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m   1769\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1770\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m_is_scalar_access\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mkey\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mTuple\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m/opt/anaconda3/lib/python3.8/site-packages/pandas/core/indexing.py\u001b[0m in \u001b[0;36m_getitem_axis\u001b[0;34m(self, key, axis)\u001b[0m\n\u001b[1;32m   1963\u001b[0m         \u001b[0;31m# fall thru to straight lookup\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1964\u001b[0m         \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_validate_key\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mkey\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0maxis\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 1965\u001b[0;31m         \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_get_label\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mkey\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0maxis\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0maxis\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m   1966\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1967\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m/opt/anaconda3/lib/python3.8/site-packages/pandas/core/indexing.py\u001b[0m in \u001b[0;36m_get_label\u001b[0;34m(self, label, axis)\u001b[0m\n\u001b[1;32m    623\u001b[0m             \u001b[0;32mraise\u001b[0m \u001b[0mIndexingError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"no slices here, handle elsewhere\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    624\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 625\u001b[0;31m         \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mobj\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_xs\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mlabel\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0maxis\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0maxis\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    626\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    627\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m_get_loc\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mkey\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mint\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0maxis\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mint\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m/opt/anaconda3/lib/python3.8/site-packages/pandas/core/generic.py\u001b[0m in \u001b[0;36mxs\u001b[0;34m(self, key, axis, level, drop_level)\u001b[0m\n\u001b[1;32m   3535\u001b[0m             \u001b[0mloc\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mnew_index\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mindex\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mget_loc_level\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mkey\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mdrop_level\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mdrop_level\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   3536\u001b[0m         \u001b[0;32melse\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 3537\u001b[0;31m             \u001b[0mloc\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mindex\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mget_loc\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mkey\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m   3538\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   3539\u001b[0m             \u001b[0;32mif\u001b[0m \u001b[0misinstance\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mloc\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mnp\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mndarray\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m/opt/anaconda3/lib/python3.8/site-packages/pandas/core/indexes/base.py\u001b[0m in \u001b[0;36mget_loc\u001b[0;34m(self, key, method, tolerance)\u001b[0m\n\u001b[1;32m   2646\u001b[0m                 \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_engine\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mget_loc\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mkey\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   2647\u001b[0m             \u001b[0;32mexcept\u001b[0m \u001b[0mKeyError\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 2648\u001b[0;31m                 \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_engine\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mget_loc\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_maybe_cast_indexer\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mkey\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m   2649\u001b[0m         \u001b[0mindexer\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mget_indexer\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mkey\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mmethod\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mmethod\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mtolerance\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mtolerance\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   2650\u001b[0m         \u001b[0;32mif\u001b[0m \u001b[0mindexer\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mndim\u001b[0m \u001b[0;34m>\u001b[0m \u001b[0;36m1\u001b[0m \u001b[0;32mor\u001b[0m \u001b[0mindexer\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0msize\u001b[0m \u001b[0;34m>\u001b[0m \u001b[0;36m1\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32mpandas/_libs/index.pyx\u001b[0m in \u001b[0;36mpandas._libs.index.IndexEngine.get_loc\u001b[0;34m()\u001b[0m\n",
      "\u001b[0;32mpandas/_libs/index.pyx\u001b[0m in \u001b[0;36mpandas._libs.index.IndexEngine.get_loc\u001b[0;34m()\u001b[0m\n",
      "\u001b[0;32mpandas/_libs/hashtable_class_helper.pxi\u001b[0m in \u001b[0;36mpandas._libs.hashtable.Int64HashTable.get_item\u001b[0;34m()\u001b[0m\n",
      "\u001b[0;32mpandas/_libs/hashtable_class_helper.pxi\u001b[0m in \u001b[0;36mpandas._libs.hashtable.Int64HashTable.get_item\u001b[0;34m()\u001b[0m\n",
      "\u001b[0;31mKeyError\u001b[0m: 2"
     ]
    }
   ],
   "source": [
    "# on the other hand, this doesn't work\n",
    "s.loc[2]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Boolean Indexing\n",
    "\n",
    "While it's good to know how to refer to rows by index, this is not the most useful way to filter data frames. Boolean indexing instead allows us to filter the rows of a data set based on one or more conditions. Boolean indexing in data frames is very similar to Boolean indexing in `numpy` arrays. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 53,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Species</th>\n",
       "      <th>Region</th>\n",
       "      <th>Island</th>\n",
       "      <th>Culmen Length (mm)</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>0</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>1</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.5</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>40.3</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>3</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>4</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>36.7</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>...</th>\n",
       "      <td>...</td>\n",
       "      <td>...</td>\n",
       "      <td>...</td>\n",
       "      <td>...</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>339</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>340</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>46.8</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>341</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>50.4</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>342</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>45.2</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>343</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>49.9</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "<p>344 rows × 4 columns</p>\n",
       "</div>"
      ],
      "text/plain": [
       "                                 Species  Region     Island  \\\n",
       "0    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "1    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "2    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "3    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "4    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "..                                   ...     ...        ...   \n",
       "339    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "340    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "341    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "342    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "343    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "\n",
       "     Culmen Length (mm)  \n",
       "0                  39.1  \n",
       "1                  39.5  \n",
       "2                  40.3  \n",
       "3                   NaN  \n",
       "4                  36.7  \n",
       "..                  ...  \n",
       "339                 NaN  \n",
       "340                46.8  \n",
       "341                50.4  \n",
       "342                45.2  \n",
       "343                49.9  \n",
       "\n",
       "[344 rows x 4 columns]"
      ]
     },
     "execution_count": 53,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "penguins"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 54,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "0       True\n",
       "1       True\n",
       "2      False\n",
       "3      False\n",
       "4       True\n",
       "       ...  \n",
       "339    False\n",
       "340    False\n",
       "341    False\n",
       "342    False\n",
       "343    False\n",
       "Name: Culmen Length (mm), Length: 344, dtype: bool"
      ]
     },
     "execution_count": 54,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "penguins['Culmen Length (mm)'] < 40"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 56,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Species</th>\n",
       "      <th>Region</th>\n",
       "      <th>Island</th>\n",
       "      <th>Culmen Length (mm)</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>0</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>1</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.5</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>4</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>36.7</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>5</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.3</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>6</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>38.9</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>...</th>\n",
       "      <td>...</td>\n",
       "      <td>...</td>\n",
       "      <td>...</td>\n",
       "      <td>...</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>146</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Dream</td>\n",
       "      <td>39.2</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>147</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Dream</td>\n",
       "      <td>36.6</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>148</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Dream</td>\n",
       "      <td>36.0</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>149</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Dream</td>\n",
       "      <td>37.8</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>150</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Dream</td>\n",
       "      <td>36.0</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "<p>100 rows × 4 columns</p>\n",
       "</div>"
      ],
      "text/plain": [
       "                                 Species  Region     Island  \\\n",
       "0    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "1    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "4    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "5    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "6    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "..                                   ...     ...        ...   \n",
       "146  Adelie Penguin (Pygoscelis adeliae)  Anvers      Dream   \n",
       "147  Adelie Penguin (Pygoscelis adeliae)  Anvers      Dream   \n",
       "148  Adelie Penguin (Pygoscelis adeliae)  Anvers      Dream   \n",
       "149  Adelie Penguin (Pygoscelis adeliae)  Anvers      Dream   \n",
       "150  Adelie Penguin (Pygoscelis adeliae)  Anvers      Dream   \n",
       "\n",
       "     Culmen Length (mm)  \n",
       "0                  39.1  \n",
       "1                  39.5  \n",
       "4                  36.7  \n",
       "5                  39.3  \n",
       "6                  38.9  \n",
       "..                  ...  \n",
       "146                39.2  \n",
       "147                36.6  \n",
       "148                36.0  \n",
       "149                37.8  \n",
       "150                36.0  \n",
       "\n",
       "[100 rows x 4 columns]"
      ]
     },
     "execution_count": 56,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "penguins[penguins['Culmen Length (mm)'] < 40]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 61,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
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       "<table border=\"1\" class=\"dataframe\">\n",
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       "      <th></th>\n",
       "      <th>Species</th>\n",
       "      <th>Region</th>\n",
       "      <th>Island</th>\n",
       "      <th>Culmen Length (mm)</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>0</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
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       "      <td>39.1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>1</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.5</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>40.3</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>3</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>4</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>36.7</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "                               Species  Region     Island  Culmen Length (mm)\n",
       "0  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.1\n",
       "1  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.5\n",
       "2  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                40.3\n",
       "3  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                 NaN\n",
       "4  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                36.7"
      ]
     },
     "execution_count": 61,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# list of penguins encountered on Torgersen island\n",
    "torg = penguins['Island']== \"Torgersen\"\n",
    "penguins[torg].head()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 66,
   "metadata": {},
   "outputs": [
    {
     "data": {
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       "      <th>Culmen Length (mm)</th>\n",
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       "  </thead>\n",
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       "    <tr>\n",
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       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
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       "      <td>39.1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>1</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.5</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>4</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>36.7</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>5</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.3</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>6</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>38.9</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "                               Species  Region     Island  Culmen Length (mm)\n",
       "0  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.1\n",
       "1  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.5\n",
       "4  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                36.7\n",
       "5  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.3\n",
       "6  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                38.9"
      ]
     },
     "execution_count": 66,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# penguins encountered on Torgersen with culmen no longer than 40 mm\n",
    "# using bitwise and operator &\n",
    "culm = penguins['Culmen Length (mm)'] < 40\n",
    "penguins[torg & culm].head()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 67,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
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       "      <th>Species</th>\n",
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       "      <th>Island</th>\n",
       "      <th>Culmen Length (mm)</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>0</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>1</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.5</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>40.3</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>3</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>4</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>36.7</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "                               Species  Region     Island  Culmen Length (mm)\n",
       "0  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.1\n",
       "1  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                39.5\n",
       "2  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                40.3\n",
       "3  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                 NaN\n",
       "4  Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen                36.7"
      ]
     },
     "execution_count": 67,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# using bitwise or instead of and\n",
    "penguins[torg | culm].head()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "An especially useful example of Boolean indexing is picking out `nan` values from the data. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 71,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
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       "\n",
       "    .dataframe tbody tr th {\n",
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       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Species</th>\n",
       "      <th>Region</th>\n",
       "      <th>Island</th>\n",
       "      <th>Culmen Length (mm)</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>3</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>339</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "                                 Species  Region     Island  \\\n",
       "3    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "339    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "\n",
       "     Culmen Length (mm)  \n",
       "3                   NaN  \n",
       "339                 NaN  "
      ]
     },
     "execution_count": 71,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "nas = penguins[\"Culmen Length (mm)\"].isna()\n",
    "penguins[nas]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 76,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
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       "      <th></th>\n",
       "      <th>Species</th>\n",
       "      <th>Region</th>\n",
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       "      <th>Culmen Length (mm)</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>0</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
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       "      <td>39.1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>1</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.5</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>40.3</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>4</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>36.7</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>5</th>\n",
       "      <td>Adelie Penguin (Pygoscelis adeliae)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Torgersen</td>\n",
       "      <td>39.3</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>...</th>\n",
       "      <td>...</td>\n",
       "      <td>...</td>\n",
       "      <td>...</td>\n",
       "      <td>...</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>338</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>47.2</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>340</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>46.8</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>341</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>50.4</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>342</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>45.2</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>343</th>\n",
       "      <td>Gentoo penguin (Pygoscelis papua)</td>\n",
       "      <td>Anvers</td>\n",
       "      <td>Biscoe</td>\n",
       "      <td>49.9</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "<p>342 rows × 4 columns</p>\n",
       "</div>"
      ],
      "text/plain": [
       "                                 Species  Region     Island  \\\n",
       "0    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "1    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "2    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "4    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "5    Adelie Penguin (Pygoscelis adeliae)  Anvers  Torgersen   \n",
       "..                                   ...     ...        ...   \n",
       "338    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "340    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "341    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "342    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "343    Gentoo penguin (Pygoscelis papua)  Anvers     Biscoe   \n",
       "\n",
       "     Culmen Length (mm)  \n",
       "0                  39.1  \n",
       "1                  39.5  \n",
       "2                  40.3  \n",
       "4                  36.7  \n",
       "5                  39.3  \n",
       "..                  ...  \n",
       "338                47.2  \n",
       "340                46.8  \n",
       "341                50.4  \n",
       "342                45.2  \n",
       "343                49.9  \n",
       "\n",
       "[342 rows x 4 columns]"
      ]
     },
     "execution_count": 76,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# invert flips the entries of a boolean array\n",
    "penguins[np.invert(nas)]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Boolean indexing is by far the most useful form of filtering, and should usually be preferred in most practical contexts. It is especially powerful when combined with functions that operate on columns, as we'll see shortly. "
   ]
  }
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