Ggplot: how to show boxplots in a given order?

Question

I have a peculiar problem with arranging boxplots given a certain order of the x-axis, as I am adding two boxplots from different dataframe in the same plot and each time I add the second geom_boxplot, R reorders my x axis alphabetically instead of following ordered levels of factor(x). So, I have two dataframe of different lengths lookings something like this:

There is always more observations per id in df1 than in df2 and there is some ids in df1 that are not available in df2.

I'd like df1 to be sorted by the median(value) (ascending) and to first plot boxplots for each id in that order. Then I add a second layer with boxplots for all other measurements per id from df2, which should maintain the same order on the x-axis. Here's how I approached that:

vec <- df %>%
  group_by(id) %>%
  summarize(m = median(value)) %>%
  arrange(m) %>%
  pull(id)

p1 <- df1 %>%
  ggplot(aes(x = factor(id, levels = vec), y = value)) +
  geom_boxplot()

p1

p2 <- p1 +
  geom_boxplot(data = df2, aes(x = factor(id, levels = vec), y = value))

p2

p1 shows the right order (ids are ordered based on ascending medians), p2 always throws my order off and goes back to plotting ids alphabetically (my id is a character column with names actually). I tried with sample dataframes and the above code achieves what is required. Hence, I am not sure what could be specifically wrong about my data so that the code fails when applied to the specific data and not the above mock data. Any ideas?

Thanks a lot in advance!

Without a reproducible example one could only guess what's the issue. What you could try is to bind both df's by row, i.e. try with bind_rows(df1, df2, .id = "df") %>% ggplot(aes(x = factor(id, levels = vec), y = value, group = interaction(id, df))) + geom_boxplot(position = "identity") — stefan
Hey! thanks for your suggestion, I followed the approach of Vinicius and it worked. Next time I'll make sure I post a reproducible example too. Thank you! — YASEM

Vinícius Félix Vinícius Félix · Accepted Answer · 2021-08-31T23:07:42

If I understood correctly, this shoud work.

library(tidyverse)


# Sample data

df1 <-
  tibble(
    id = c("A","A","A","A","B","B","B","C","C"),
    value = c(1,2,3,5,10,8,1,3,7),
    type = "df1"
  )


df2 <-
  tibble(
    id = c("A","A","B","B"),
    value = c(4,5,6,8),
    type = "df2"
  )


df <-
  # Create single data.frame
  df1 %>% 
  bind_rows(df2) %>% 
  # Reorder id by median(value)
  mutate(id = fct_reorder(id,value,median))

df %>%
  ggplot(aes(id, y = value, fill = type)) +
  geom_boxplot()

Ggplot: how to show boxplots in a given order?

1 Answers