This post describes how to reorder a variable in a ggplot2
chart. Several methods are suggested, always providing examples with reproducible code chunks.
Reordering groups in a ggplot2
chart can be a struggle. This is due to the fact that ggplot2 takes into account the order of the factor
levels, not the order you observe in your data frame. You can sort your input data frame with sort()
or arrange()
, it will never have any impact on your ggplot2
output.
This post explains how to reorder the level of your factor through several examples. Examples are based on 2 dummy datasets:
# Library
library(ggplot2)
library(dplyr)
# Dataset 1: one value per group
data <- data.frame(
name=c("north","south","south-east","north-west","south-west","north-east","west","east"),
val=sample(seq(1,10), 8 )
)
# Dataset 2: several values per group (natively provided in R)
# mpg
Forecats
libraryThe Forecats library is a library from the tidyverse especially made to handle factors in R. It provides a suite of useful tools that solve common problems with factors. The fact_reorder()
function allows to reorder the factor (data$name
for example) following the value of another column (data$val
here).
# load the library
library(forcats)
# Reorder following the value of another column:
data %>%
mutate(name = fct_reorder(name, val)) %>%
ggplot( aes(x=name, y=val)) +
geom_bar(stat="identity", fill="#f68060", alpha=.6, width=.4) +
coord_flip() +
xlab("") +
theme_bw()
# Reverse side
data %>%
mutate(name = fct_reorder(name, desc(val))) %>%
ggplot( aes(x=name, y=val)) +
geom_bar(stat="identity", fill="#f68060", alpha=.6, width=.4) +
coord_flip() +
xlab("") +
theme_bw()
If you have several values per level of your factor, you can specify which function to apply to determine the order. The default is to use the median, but you can use the number of data points per group to make the classification:
# Using median
mpg %>%
mutate(class = fct_reorder(class, hwy, .fun='median')) %>%
ggplot( aes(x=reorder(class, hwy), y=hwy, fill=class)) +
geom_boxplot() +
xlab("class") +
theme(legend.position="none") +
xlab("")
# Using number of observation per group
mpg %>%
mutate(class = fct_reorder(class, hwy, .fun='length' )) %>%
ggplot( aes(x=class, y=hwy, fill=class)) +
geom_boxplot() +
xlab("class") +
theme(legend.position="none") +
xlab("") +
xlab("")
The last common operation is to provide a specific order to your levels, you can do so using the fct_relevel()
function as follow:
dplyr
onlyThe mutate()
function of dplyr
allows to create a new variable or modify an existing one. It is possible to use it to recreate a factor with a specific order. Here are 2 examples:
arrange()
to sort your data frame, and reorder the factor following this desired order.data %>%
arrange(val) %>% # First sort by val. This sort the dataframe but NOT the factor levels
mutate(name=factor(name, levels=name)) %>% # This trick update the factor levels
ggplot( aes(x=name, y=val)) +
geom_segment( aes(xend=name, yend=0)) +
geom_point( size=4, color="orange") +
coord_flip() +
theme_bw() +
xlab("")
data %>%
arrange(val) %>%
mutate(name = factor(name, levels=c("north", "north-east", "east", "south-east", "south", "south-west", "west", "north-west"))) %>%
ggplot( aes(x=name, y=val)) +
geom_segment( aes(xend=name, yend=0)) +
geom_point( size=4, color="orange") +
theme_bw() +
xlab("")
reorder()
function of base RIn case your an unconditional user of the good old R, here is how to control the order using the reorder()
function inside a with()
call: