Adding a line at the mean of the data, ggplot2

Question

I am trying to add a simple line to show the median and mean of my data in a ggplot2 bar chart.

Here is the code I have

library(ggplot2)
library(plyr)

data <- c(1,1,1,2,2,2,2,2,2,3,3,4,5)

count_data<- count(data)

mean <- mean(count_data)
med <- median(count_data)
ggplot(count_data) + 
  geom_bar(aes(x=x, y=freq), stat="identity", position="dodge") +
  geom_vline(aes(xintercept=mean)) + 
  #facet_wrap(~Year, nrow=1) + 
  theme_classic()

I do see my data alright, but the vline does not show up. Would you know what's wrong?

Which package's `count` function are you using in line 2 - `plyr`? — Jon Spring, Dec 27 '18 at 17:13
Did you mean `mean <- mean(data); med <- median(data)`? I get an error when I run those on `count_data`. — Jon Spring, Dec 27 '18 at 17:16
Damn, silly me, that was indeed the problem. Thanks for solving that :) — LBes, Dec 27 '18 at 17:16

score 2 · Accepted Answer · answered Dec 27 '18 at 17:22

I'm assuming you want the mean/median frequency, given you have created count_data. To do this I have explicitly called the freq variable when creating mean and med. The below therefore has both lines on the barplot.

If you actually want the mean/median of data, then it should just be mean(data), for example.

data <- c(1,1,1,2,2,2,2,2,2,3,3,4,5)

count_data<- plyr::count(data)

mean <- mean(count_data$freq)
med <- median(count_data$freq)
ggplot(count_data) + 
  geom_bar(aes(x=x, y=freq), stat="identity", position="dodge") +
  geom_vline(aes(xintercept = mean)) + 
  geom_vline(aes(xintercept = med)) +
  #facet_wrap(~Year, nrow=1) + 
  theme_classic()

Great solution. You don't need to calculate the mean and median first, you can do this directly in the code to the same effect: *p + geom_vline(xintercept = mean(freq))* — glenn_in_boston, Feb 03 '22 at 16:33

Adding a line at the mean of the data, ggplot2

1 Answers1