Boxplot show the value of mean

Question

In this boxplot we can see the mean but how can we have also the number value on the plot for every mean of every box plot?

 ggplot(data=PlantGrowth, aes(x=group, y=weight, fill=group)) + geom_boxplot() +
     stat_summary(fun.y=mean, colour="darkred", geom="point", 
                           shape=18, size=3,show_guide = FALSE)

+1 for short, self-contained, reproducible example. – Simon O'Hanlon Nov 09 '13 at 13:37 — Simon O'Hanlon, Nov 09 '13 at 13:37
Duplicate of http://stackoverflow.com/q/15660829/1036500 – Ben Nov 09 '13 at 17:34 — Ben, Nov 09 '13 at 17:34

score 104 · Accepted Answer · edited Mar 03 '21 at 18:22

104

First, you can calculate the group means with aggregate:

means <- aggregate(weight ~  group, PlantGrowth, mean)

This dataset can be used with geom_text:

library(ggplot2)
ggplot(data=PlantGrowth, aes(x=group, y=weight, fill=group)) + geom_boxplot() +
  stat_summary(fun=mean, colour="darkred", geom="point", 
               shape=18, size=3, show.legend=FALSE) + 
  geom_text(data = means, aes(label = weight, y = weight + 0.08))

Here, + 0.08 is used to place the label above the point representing the mean.

enter image description here

An alternative version without ggplot2:

means <- aggregate(weight ~  group, PlantGrowth, mean)

boxplot(weight ~ group, PlantGrowth)
points(1:3, means$weight, col = "red")
text(1:3, means$weight + 0.08, labels = means$weight)

edited Mar 03 '21 at 18:22

stefan

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answered Nov 09 '13 at 13:43

Sven Hohenstein

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+1 - I had just worked this through and came to update my answer and BAM!. Well done. – Simon O'Hanlon Nov 09 '13 at 13:46
How can you decrease the size of the text? – Martin Velez Feb 26 '14 at 04:27
Also, how can you limit the number of decimals? – Martin Velez Feb 26 '14 at 04:28
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@MartinVelez For example, `geom_text(data = means, aes(label = round(weight, 1), y = weight + 0.08), size = 3)` creates smaller text with 1 decimal place. – Sven Hohenstein Feb 26 '14 at 07:43
@SvenHohenstein Thanks! I am using `formatC(weight,2)`. – Martin Velez Feb 26 '14 at 08:06
@SvenHohenstein is it possible to do this without ggplot? – Herman Toothrot Oct 26 '15 at 15:24
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@user4050 I added a section on how to create a similar plot without `ggplot2`. See the update. – Sven Hohenstein Oct 26 '15 at 18:51
@ Sven Hohenstein thank you, it was very helpful. I have one problem: when I used that line to show means of categories divided by gender the meanes were stacked in the same vertical axis, instead of being in the correspondent boxplot. How can correct that? – mad Mar 09 '17 at 19:54
@mad This is hard to answer without knowing the `ggplot2` command. – Sven Hohenstein Mar 09 '17 at 19:58
@ Sven Hohenstein I'm sorry, below is the ggplot2 command: ggplot(ggchen[(4045*12+1):(4045*15),], aes(Rank, Eval, fill=Gen)) + geom_boxplot() + facet_grid(. ~ Question) + stat_summary(fun.y=mean, colour="darkred", geom="point", shape=18, size=3, show_guide=FALSE) https://ibb.co/gOoZtv <-- image – mad Mar 09 '17 at 20:01
1

@mad Try to add the argument `position = position_dodge(width = 3/4)` to `stat_summary`. – Sven Hohenstein Mar 09 '17 at 20:21

score 38 · Answer 2 · edited Dec 16 '14 at 18:07

38

You can use the output value from stat_summary()

ggplot(data=PlantGrowth, aes(x=group, y=weight, fill=group)) 
+ geom_boxplot() 
+ stat_summary(fun.y=mean, colour="darkred", geom="point", hape=18, size=3,show_guide = FALSE)
+ stat_summary(fun.y=mean, colour="red", geom="text", show_guide = FALSE, 
               vjust=-0.7, aes( label=round(..y.., digits=1)))

edited Dec 16 '14 at 18:07

Pieter Meiresone

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answered Jun 17 '14 at 14:52

user3749036

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I also want to add mean in the boxplots. So, I amended by box plot code by adding `stat_summary()` & `fill=x` but getting this error: `Error: Unknown parameters: hape In addition: Warning message:show_guide has been deprecated. Please use show.legend instead. ` What's wrong in your code? – Aby Oct 06 '16 at 09:58
I like this answer, because it doesn't make a new table or write a new function, but instead uses a built-in feature of `ggplot2` in the way `ggplot2` was designed, imho, namely `fun.y=mean, ... , geom="text"`. I just had to put the `+` signs at the ends of lines instead of the beginnings, so there is that issue, but that's an easy and obvious fix. – jena Oct 20 '21 at 17:17

score 17 · Answer 3 · answered Nov 11 '13 at 10:30

You can also use a function within stat_summary to calculate the mean and the hjust argument to place the text, you need a additional function but no additional data frame:

fun_mean <- function(x){
  return(data.frame(y=mean(x),label=mean(x,na.rm=T)))}


ggplot(PlantGrowth,aes(x=group,y=weight)) +
geom_boxplot(aes(fill=group)) +
stat_summary(fun.y = mean, geom="point",colour="darkred", size=3) +
stat_summary(fun.data = fun_mean, geom="text", vjust=-0.7)

enter image description here

jena · Answer 4 · 2020-10-13T16:43:30.420

The Magrittr way

I know there is an accepted answer already, but I wanted to show one cool way to do it in single command with the help of magrittr package.

PlantGrowth %$% # open dataset and make colnames accessible with '$'
split(weight,group) %T>% # split by group and side-pipe it into boxplot
boxplot %>% # plot
lapply(mean) %>% # data from split can still be used thanks to side-pipe '%T>%'
unlist %T>% # convert to atomic and side-pipe it to points
points(pch=18)  %>% # add points for means to the boxplot
text(x=.+0.06,labels=.) # use the values to print text

This code will produce a boxplot with means printed as points and values:

I split the command on multiple lines so I can comment on what each part does, but it can also be entered as a oneliner. You can learn more about this in my gist.

Boxplot show the value of mean

4 Answers4

The Magrittr way

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