How do I add SE error bars to my barplot in ggplot

Question

I made a simple barplot with ggplot2 comparing the mean lifespan (age) of males and females for 2 insect species. My code looks like this, with "dataset" being, well, my data set...

    gplot(dataset, aes(Species, Age, fill=Sex))+
stat_summary(fun.y = mean, geom = "bar", position = "dodge")+
scale_fill_manual(values = c("Grey25", "Grey"))+
theme(legend.title = element_blank())+
scale_y_continuous(limits = c(0,15))

I tried using the following code to manually enter the value of the mean±SE to set the limits for the error bar. For the sake of simplicity, let's assume mean=10 and SE=0.5 for males of species1.

geom_errorbar(aes(ymin=9.5, ymax=10.5),width=.2,position=position_dodge(.9))

This code does indeed work, but it sets the same error bars for each bar in my plot.

How can I add error bars equal to the corresponding SE for each bar in my plot?

I am fairly new to ggplot and R in general so any help/advice is welcome.

Answer 1

You don't need more than to add stat_summary(geom = "errorbar", fun.data = mean_se, position = "dodge") to your plot:

library(ggplot2)

ggplot(diamonds, aes(cut, price, fill = color)) +
  stat_summary(geom = "bar", fun.y = mean, position = "dodge") +
  stat_summary(geom = "errorbar", fun.data = mean_se, position = "dodge")

If you prefer to calculate the values beforehand, you could do it like this:

library(tidyverse)
pdata <- diamonds %>% 
  group_by(cut, color) %>% 
  summarise(new = list(mean_se(price))) %>% 
  unnest(new)


pdata %>% 
  ggplot(aes(cut, y = y, fill = color)) +
  geom_col(position = "dodge") +
  geom_errorbar(aes(ymin = ymin, ymax = ymax), position = "dodge")

Answer 2

You can add an error bar on your barplot with the geom_errorbar geom.

You need to supply the ymin and ymax, so you need to compute it manually.

From the geom_errorbar help page :

p + geom_errorbar(aes(ymin = lower, ymax = upper), width = 0.2)

Colin