Often you may want to create a histogram that has several different colors in R.
The following examples show how to do so in base R and in ggplot2.
Example 1: Histogram with Different Colors in Base R
The following code shows how to create a histogram with just one color in base R:
#create data frame
df <- data.frame(x=c(12, 14, 14, 15, 15, 17, 19, 22, 23, 23, 24))
#create histogram
hist(df$x)
By default, all of the colors of the bars are the same in the histogram.
However, we can use the following code to create a histogram with three different colors:
#create data frame
df <- data.frame(x=c(12, 14, 14, 15, 15, 17, 19, 22, 23, 23, 24))
#define histogram break points
hist_breaks <- hist(df$x)$breaks
#define colors to use in histogram based on break points
color_list <- rep('red', length(hist_breaks))
color_list[hist_breaks < 20] <- 'blue'
color_list[hist_breaks < 16] <- 'purple'
#create histogram with custom colors
hist(df$x, col=color_list)
Here’s how the logic worked to create the three colors:
- First, we specified every bar to be red.
- Then, we changed every bar with a break point less than 20 to be blue.
- Then, we changed every bar with a break point less than 16 to be purple.
The end result is a histogram with three colors.
Example 2: Histogram with Different Colors in ggplot2
Suppose we have the following data frame in R:
#create data frame
df <- data.frame(x=c(12, 14, 14, 15, 15, 17, 19, 22, 23, 23, 24))
#view data frame
df
x
1 12
2 14
3 14
4 15
5 15
6 17
7 19
8 22
9 23
10 23
11 24
To create a histogram with different colors for this data frame, we need to first create a grouping variable for the values using a nested if else statement:
#create grouping variable
df$group = ifelse(df$x < 16, 'C', ifelse(df$x < 20, 'B', 'A'))
#view updated data frame
df
x group
1 12 C
2 14 C
3 14 C
4 15 C
5 15 C
6 17 B
7 19 B
8 22 A
9 23 A
10 23 A
11 24 A
Now we can create a histogram in ggplot2 and define the colors in the plot using the group variable:
#create histogram with custom colors
ggplot(df, aes(x, fill=group)) +
geom_histogram(bins=6, color='black') +
scale_fill_manual(values = c('A' = 'red',
'B' = 'blue',
'C' = 'purple'))
The end result is a histogram with three colors.
Note: You can find the complete documentation for scale_fill_manual() here.
Additional Resources
The following tutorials explain how to perform other common operations in R:
How to Create a Relative Frequency Histogram in R
How to Overlay Normal Curve on Histogram in R
How to Specify Histogram Breaks in R