R Language boxplot Create a box-and-whisker plot with boxplot() {graphics}
Example
This example use the default boxplot() function and the irisdata frame.
> head(iris)
Sepal.Length Sepal.Width Petal.Length Petal.Width Species
1 5.1 3.5 1.4 0.2 setosa
2 4.9 3.0 1.4 0.2 setosa
3 4.7 3.2 1.3 0.2 setosa
4 4.6 3.1 1.5 0.2 setosa
5 5.0 3.6 1.4 0.2 setosa
6 5.4 3.9 1.7 0.4 setosa
Simple boxplot (Sepal.Length)
Create a box-and-whisker graph of a numerical variable
boxplot(iris[,1],xlab="Sepal.Length",ylab="Length(in centemeters)",
main="Summary Charateristics of Sepal.Length(Iris Data)")
Boxplot of sepal length grouped by species
Create a boxplot of a numerical variable grouped by a categorical variable
boxplot(Sepal.Length~Species,data = iris)
Bring order
To change order of the box in the plot you have to change the order of the categorical variable's levels.
For example if we want to have the order virginica - versicolor - setosa
newSpeciesOrder <- factor(iris$Species, levels=c("virginica","versicolor","setosa"))
boxplot(Sepal.Length~newSpeciesOrder,data = iris)
Change groups names
If you want to specifie a better name to your groups you can use the Names parameter. It take a vector of the size of the levels of categorical variable
boxplot(Sepal.Length~newSpeciesOrder,data = iris,names= c("name1","name2","name3"))
Small improvements
Color
col : add a vector of the size of the levels of categorical variable
boxplot(Sepal.Length~Species,data = iris,col=c("green","yellow","orange"))
Proximity of the box
boxwex: set the margin between boxes.
Left boxplot(Sepal.Length~Species,data = iris,boxwex = 0.1)
Right boxplot(Sepal.Length~Species,data = iris,boxwex = 1)
See the summaries which the boxplots are based plot=FALSE
To see a summary you have to put the paramater plot to FALSE.
Various results are given
> boxplot(Sepal.Length~newSpeciesOrder,data = iris,plot=FALSE)
$stats #summary of the numerical variable for the 3 groups
[,1] [,2] [,3]
[1,] 5.6 4.9 4.3 # extreme value
[2,] 6.2 5.6 4.8 # first quartile limit
[3,] 6.5 5.9 5.0 # median limit
[4,] 6.9 6.3 5.2 # third quartile limit
[5,] 7.9 7.0 5.8 # extreme value
$n #number of observations in each groups
[1] 50 50 50
$conf #extreme value of the notchs
[,1] [,2] [,3]
[1,] 6.343588 5.743588 4.910622
[2,] 6.656412 6.056412 5.089378
$out #extreme value
[1] 4.9
$group #group in which are the extreme value
[1] 1
$names #groups names
[1] "virginica" "versicolor" "setosa"
