Create Boxplot with respect to two factors using ggplot2 in R

Multiple variable distributions can be visualized with boxplots. ggplot2 allows us to create beautiful boxplots quickly. It is possible to have multiple subgroups for a variable of interest. In those situations, it is very useful to visualize using “grouped boxplots”. The ggplot2 package in R programming language provides a number of options for visualizing such grouped boxplots. 

Now talking about Boxplot, then each boxplot is created for every category or level in that factor that is represented by a factor and a numerical column. geom_boxplot also allows us to plot both factors using the fill argument when there are two factors. Geom_boxplot() is the key function

Syntax: 

geom_boxplot(width,notch,color,size,linetype, fill,outliner.color, outliner.size, outliner.shape)

Parameter:

• width: width of the boxplot
• notch: if it is true then it will create a notched boxplot and notches are used to compare boxplots.
• color, size,line type: borderline, color, size and shape.
• fill: used to fill box plot areas.
• outlier.colour, outlier.shape, outlier.size: The color, the shape and the size for outlying points.

Now let us look at few implementations.

Example 1:

R

# create a Data Frame
Gender<-sample(c("Male","Female"),20,replace=TRUE)
Values<-rnorm(20,mean=0,sd=1)
Group<-sample(letters[1:5],20,replace=TRUE)

df<-data.frame(Gender,Values,Group)

library(ggplot2)

# creating a boxplot
ggplot(df,aes(Gender,Values))+geom_boxplot(aes(fill=Group))

Output:

Example 2:

R

# load ggplot2 package if already installed
library(ggplot2)

# create a data frame with two factors
df <- data.frame(Factor1=factor(rbinom(30, 1, 0.55),
                                label=c("male","female")),
                   Factor2=factor(rbinom(30, 1, 0.45),
                                  label=c("young","old")),
                   Values=rnorm(30,mean=5,sd=2))

# Now make a interaction between two factors
# on x axis
df$Factor1Factor2 <- interaction(df$Factor1, df$Factor2)

# now Plot Boxplot with fill color according
# to factor1 and factor2
ggplot(aes(y = Values, x = Factor1Factor2), data = df) +
geom_boxplot(aes(fill=Factor1Factor2))

Output: