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   "cell_type": "markdown",
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   "source": [
    "# List comprehension practice\n",
    "## 1. Stemming words"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Consider the following list of activities."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "activities = ['running', 'jumping', 'shouting', 'dancing', 'singing', 'eating', 'reading']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "In this exercise, we will:\n",
    "- remove the `ing` from the end of every activity\n",
    "- add a dash `-` to each activity\n",
    "- sort the result\n",
    "- join the activities into a single string using the delimiter `|`\n",
    "\n",
    "To start, I have added a simple comprehension that just copies the list.    \n",
    "- `for a in activities`, it returns `a`"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   },
   "outputs": [],
   "source": [
    "# The following list comprehension just returns every activity in the list of activities\n",
    "[a for a in activities]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "1. Modify the comprehension so it returns every activity with the last three letters removed. You'll want to get:   \n",
    "\n",
    "        ['runn', 'jump', 'shout', 'danc', 'sing', 'eat', 'read']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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   "outputs": [],
   "source": [
    "# Copy comprehension above, modify to remove last three letters\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Answer:** <span style=\"color:white\"> [a[:-3] for a in activities]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "2. Now, add a dash after each element in the list to get:\n",
    "\n",
    "        ['runn-', 'jump-', 'shout-', 'danc-', 'sing-', 'eat-', 'read-']  "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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   "outputs": [],
   "source": [
    "# Copy comprehension above, modify to add a dash \n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Answer:** <span style=\"color:white\"> [a[:-3]+\"-\" for a in activities]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "3. Now, sort the list to get:\n",
    "\n",
    "       ['danc-', 'eat-', 'jump-', 'read-', 'runn-', 'shout-', 'sing-']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   "outputs": [],
   "source": [
    "# Copy comprehension above, sort it\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Answer:** <span style=\"color:white\"> sorted([a[:-3]+\"-\" for a in activities])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "4. Now, merge the list back into a string to get:\n",
    "\n",
    "       'danc- | eat- | jump- | read- | runn- | shout- | sing-'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   "outputs": [],
   "source": [
    "# Copy comprehension above, join with a pipe character '|'\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Answer:** <span style=\"color:white\">' | '.join(sorted([a[:-3]+\"-\" for a in activities]))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2. Filtering lists"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The following exercise is taken from a short poem, \"The Fourth\", written by Shel Silverstein."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   "outputs": [],
   "source": [
    "fourth = [\"Oh\", \"CRASH!\", \"my\", \"BASH!\", \"it’s\", \"BANG!\", \"the\", \"ZANG!\", \"Fourth\", \"WHOOSH!\", \"of\", \"BAROOM!\", \"July\", \"WHEW!\"]\n",
    "print(\"\\n\".join(fourth))       "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Let's write a list comprehension to:\n",
    "- Remove all of the firework sounds\n",
    "- Keep only firework sounds, without exclamation points and in lower case\n",
    "\n",
    "To start, I have added a simple comprehension that just copies all the words in the list."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
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   "outputs": [],
   "source": [
    "# The following comprehension lists all the words in the fourth of July poem\n",
    "[w for w in fourth]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Modify the list comprehension to list only words without an exclamation point.    \n",
    "You will need to use an `if` filter. The result should be:\n",
    "\n",
    "    ['Oh', 'my', 'it’s', 'the', 'Fourth', 'of', 'July']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   "outputs": [],
   "source": [
    "# Modify the list comprehension above, to list only words without an exclamation point\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Answer:** <span style=\"color:white\"> [w for w in fourth if \"!\" not in w]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Join the result into a single sentence, using spaces as the join character. The result should be:\n",
    "   \n",
    "    'Oh my it’s the Fourth of July'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   "outputs": [],
   "source": [
    "# Modify the list comprehension above, joining on spaces to create a single message\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Answer:** <span style=\"color:white\"> \" \".join([w for w in fourth if \"!\" not in w])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now, write a list comprehension to list only words that **do** include an exclamation point. The answer should be:\n",
    "       \n",
    "    ['CRASH!', 'BASH!', 'BANG!', 'ZANG!', 'WHOOSH!', 'BAROOM!', 'WHEW!']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Write a list comprehension to list only words that include an exclamation point\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Answer:** <span style=\"color:white\">  [w for w in fourth if \"!\" in w]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now, edit the list comprehension above to ensure the words are all lowercase, to get:\n",
    "\n",
    "    ['crash!', 'bash!', 'bang!', 'zang!', 'whoosh!', 'baroom!', 'whew!']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Modify the list comprehension above, to make the words lowercase\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Answer:** <span style=\"color:white\">  [w.lower() for w in fourth if \"!\" in w]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Finally, edit the comprehension above to remove the exclamation point. You should end with: \n",
    "\n",
    "    ['crash', 'bash', 'bang', 'zang', 'whoosh', 'baroom', 'whew']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# And remove the exclamation point\n",
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Answer:** <span style=\"color:white\"> [w.lower()[:-1] for w in fourth if \"!\" in w]"
   ]
  }
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