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In ggplot2, the order of facets can be changed by using the “facet_wrap()” function. This function takes an argument called “scales” which can be used to specify the order in which the facets are arranged. For example, if we wanted to display the facets in descending order, we could use the “scales = ‘free_x'” argument, which would allow us to order the facets as we desired. This can be a useful feature to customize the look and feel of your plot.
You can use the following basic syntax to specify the order of facets in ggplot2:
p +
facet_grid(~factor(my_variable, levels=c('val1', 'val2', 'val3', ...)))
The following example shows how to use this syntax in practice.
Example: Change Order of Facets in ggplot2
Suppose we have the following data frame in R:
#create data frame
df <- data.frame(team=c('A', 'A', 'B', 'B', 'C', 'C', 'D', 'D'),
points=c(8, 14, 20, 22, 25, 29, 30, 31),
assists=c(10, 5, 5, 3, 8, 6, 9, 12))
#view data frame
df
team points assists
1 A 8 10
2 A 14 5
3 B 20 5
4 B 22 3
5 C 25 8
6 C 29 6
7 D 30 9
8 D 31 12
The following code shows how to use facet_grid() to create a grid that displays a scatterplot of assists vs. points for each team:
library(ggplot2)
#create multiple scatter plots using facet_grid
ggplot(df, aes(assists, points)) +
geom_point() +
facet_grid(.~team)
By default, ggplot2 places the scatter plots in order based on which values appear first in the team variable in the data frame.
However, we can convert team to a factor variable and use the levels argument to specify the order that the teams should be placed in the plot:
library(ggplot2)
#create multiple scatter plots using facet_grid with specific order
ggplot(df, aes(assists, points)) +
geom_point() +
facet_grid(~factor(team, levels=c('C', 'D', 'A', 'B')))
Notice that the scatter plots are now in order based on the order we specified within the levels argument: C, D, A, B.
The advantage of using this approach is that we don’t actually modify the underlying data.
Instead, we only change the levels within the facet_grid() function.