# Box Plots - R Base Graphs

Previously, we described the essentials of R programming and provided quick start guides for importing data into **R**.

**box plots**in R.

# Pleleminary tasks

**Launch RStudio**as described here: Running RStudio and setting up your working directory**Prepare your data**as described here: Best practices for preparing your data and save it in an external .txt tab or .csv files**Import your data**into**R**as described here: Fast reading of data from txt|csv files into R: readr package.

Here, we’ll use the R built-in ToothGrowth data set.

```
# Print the first 6 rows
head(ToothGrowth, 6)
```

```
## len supp dose
## 1 4.2 VC 0.5
## 2 11.5 VC 0.5
## 3 7.3 VC 0.5
## 4 5.8 VC 0.5
## 5 6.4 VC 0.5
## 6 10.0 VC 0.5
```

# R base box plots: boxplot()

Draw a box plot of teeth length (*len*):

**Basic box plots**

```
# Box plot of one variable
boxplot(ToothGrowth$len)
# Box plots by groups (dose)
# remove frame
boxplot(len ~ dose, data = ToothGrowth, frame = FALSE)
# Horizontal box plots
boxplot(len ~ dose, data = ToothGrowth, frame = FALSE,
horizontal = TRUE)
# Notched box plots
boxplot(len ~ dose, data = ToothGrowth, frame = FALSE,
notch = TRUE)
```

Notch is used to compare groups. In the notched boxplot, if two boxes’ notches do not overlap this is “strong evidence” their medians differ (Chambers et al., 1983, p. 62).

**Change group names**

```
boxplot(len ~ dose, data = ToothGrowth, frame = FALSE,
names = c("D0.5", "D1", "D2"))
```

**Change color**

```
# Change the color of border using one single color
boxplot(len ~ dose, data = ToothGrowth, frame = FALSE,
border = "steelblue")
# Change the color of border.
# Use different colors for each group
boxplot(len ~ dose, data = ToothGrowth, frame = FALSE,
border = c("#999999", "#E69F00", "#56B4E9"))
# Change fill color : single color
boxplot(len ~ dose, data = ToothGrowth, frame = FALSE,
col = "steelblue")
# Change fill color: multiple colors
boxplot(len ~ dose, data = ToothGrowth, frame = FALSE,
col = c("#999999", "#E69F00", "#56B4E9"))
```

**Box plot with multiple groups**

```
boxplot(len ~ supp*dose, data = ToothGrowth,
col = c("white", "steelblue"), frame = FALSE)
```

**Change main title and axis labels**

```
# Change axis titles
# Change color (col = "gray") and remove frame
# Create notched box plot
boxplot(len ~ dose, data = ToothGrowth,
main = "Plot of length by dose",
xlab = "Dose (mg)", ylab = "Length",
col = "lightgray", frame = FALSE)
```

# Box plot with the number of observations: gplots::boxplot2()

The function **boxplot2**()[in **gplots** package] can be used to create a box plot annotated with the number of observations.

Install **gplots**:

`install.packages("gplots")`

Use **boxplot2**() [in gplots]:

```
library("gplots")
# Box plot with annotation
boxplot2(len ~ dose, data = ToothGrowth,
frame = FALSE)
```

```
# Put the annotation at the top
boxplot2(len ~ dose, data = ToothGrowth,
frame = FALSE, top = TRUE)
```

# Summary

- Create basic box plots:

`boxplot(len ~ dose, data = ToothGrowth, frame = FALSE)`

- Box plots with number of observations:

```
gplots::boxplot2(len ~ dose, data = ToothGrowth,
frame = FALSE, top = TRUE)
```

# See also

# Infos

This analysis has been performed using **R statistical software** (ver. 3.2.4).

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