---
layout: post
title: "ggplot2: qplot()"
published: yes
---

## Dữ liệu

```{r data}
library(ggplot2)
head(diamonds)
set.seed(1410)
dsmall <- diamonds[sample(nrow(diamonds), 100), ]
```

## Lệnh cơ bản

```{r basic use}
# Basic use
qplot(carat, price, data = diamonds)
qplot(log(carat), log(price), data = diamonds)
qplot(carat, x * y * z, data = diamonds)
```

## Các thuộc tính thẩm mỹ

```{r other aesthetic}
# Color and shape
qplot(carat, price, data = dsmall, colour = color)
qplot(carat, price, data = dsmall, shape = cut)

# Alpha aesthetic
qplot(carat, price, data = diamonds, alpha = I(1/10))
qplot(carat, price, data = diamonds, alpha = I(1/100))
qplot(carat, price, data = diamonds, alpha = I(1/200))

# Add smoother
qplot(carat, price, data = dsmall, geom = c("point", "smooth"))
qplot(carat, price, data = diamonds, geom = c("point", "smooth"))
```

## Các đối tượng hình học

### Thêm `smoother`

```{r smoother}
# method = "loess", default for n < 1000
qplot(carat, price, data = dsmall, geom = c("point", "smooth"), 
  span = 0.2)
qplot(carat, price, data = dsmall, geom = c("point", "smooth"),
  span = 1)

# method = "gam", default for n > 1000
qplot(carat, price, data = dsmall, geom = c("point", "smooth"),
  method = "gam", formula = y ~ s(x))
qplot(carat, price, data = dsmall, geom = c("point", "smooth"),
  method = "gam", formula = y ~ s(x, bs = "cs"))

# method = "lm"
qplot(carat, price, data = dsmall, geom = c("point", "smooth"),
  method = "lm")

library(splines)
qplot(carat, price, data = dsmall, geom = c("point", "smooth"),
  method = "lm", formula = y ~ ns(x,5))

# method = "rlm"
library(MASS)
qplot(carat, price, data = dsmall, geom = c("point", "smooth"),
  method = "rlm")
```

### Boxplots và jittered points

```{r boxplot and jitter}
# Basic command
qplot(color, price / carat, data = diamonds, geom = "jitter")
qplot(color, price / carat, data = diamonds, geom = "boxplot")

# More colorful?
qplot(color, price / carat, data = diamonds, geom = "jitter",
  color = color)
qplot(color, price / carat, data = diamonds, geom = "boxplot",
  fill = color)

# Add semi-transparent
qplot(color, price / carat, data = diamonds, geom = "jitter", 
  alpha = I(1 / 5))
qplot(color, price / carat, data = diamonds, geom = "jitter", 
  alpha = I(1 / 50))
qplot(color, price / carat, data = diamonds, geom = "jitter", 
  alpha = I(1 / 200))
```

### Hoành đồ và mật độ

```{r histo & densi}
# basic
qplot(carat, data = diamonds, geom = "histogram")
qplot(carat, data = diamonds, geom = "density")

# add binwidth & xlim
qplot(carat, data = diamonds, geom = "histogram", binwidth = 1,
  xlim = c(0,3))
qplot(carat, data = diamonds, geom = "histogram", binwidth = 0.1,
  xlim = c(0,3))
qplot(carat, data = diamonds, geom = "histogram", binwidth = 0.01,
  xlim = c(0,3))

# more colorful?
qplot(carat, data = diamonds, geom = "density", colour = color)
qplot(carat, data = diamonds, geom = "histogram", fill = color)
```

### Biểu đồ cột

```{r bar chart}
# simple version
qplot(color, data = diamonds, geom = "bar")

# weighted version (by carat)
qplot(color, data = diamonds, geom = "bar", weight = carat) +
  scale_y_continuous("carat")

# more colorful?
qplot(color, data = diamonds, geom = "bar", fill = color)
```

### Chuỗi thời gian

```{r time series}
# with line
qplot(date, unemploy / pop, data = economics, geom = "line")
qplot(date, uempmed, data = economics, geom = "line")

# with path
year <- function(x) as.POSIXlt(x)$year + 1900
qplot(unemploy / pop, uempmed, data = economics,
  geom = c("point", "path"))
qplot(unemploy / pop, uempmed, data = economics,
  geom = "path", color = year(date)) + scale_size_area()
```

## Faceting

```{r faceting}
# facets
qplot(carat, data = diamonds, facets = color ~ .,
  geom = "histogram", binwidth = 0.1, xlim = c(0, 3))
# with ..density..
qplot(carat, ..density.., data = diamonds, facets = color ~ .,
  geom = "histogram", binwidth = 0.1, xlim = c(0, 3))
```

## Các tùy chọn khác

```{r other opts}
qplot(
  carat, price, data = dsmall,
  xlab = "Price ($)", ylab = "Weight (carats)",
  main = "Price-weight relationship"
)

qplot(
  carat, price/carat, data = dsmall,
  ylab = expression(frac(price,carat)),
  xlab = "Weight (carats)",
  main="Small diamonds",
  xlim = c(.2,1)
)

qplot(carat, price, data = dsmall, log = "xy")
```