Adding percentiles and summary statistics to ggplot boxplot

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Looking for some help with adding summary statistics like 0.25 and 0.75 percentile lines to ggplot boxplot.

My current code is as follows:

ggplot(aes(y = HT, x = LOCATION, fill = LOCATION, na.rm = TRUE), data = HD1) + geom_boxplot(notch = TRUE) +
  scale_fill_manual(breaks = c("NVRN", "PCN"), values=c("sky blue", "red"))+
  coord_cartesian(ylim=c(0,80)) +
  geom_smooth(method="lm") + theme_bw() + theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank())

My data is quite simple with one response and one predictor - the predictor has two categorical groups (2 locations) and I need to add the summary statistics directly onto the ggplot.

I have tried using different functions like add_summary and stat_summary to add percentile lines (in red) and means for both groups onto my ggplot. I cannot seem to figure out exactly how to do this with my code, any help would be much appreciated.

I hope this is enough information.

Thanks in advance

summary boxplot ggplot2 percentile r
1 Answers

Here is a solution.
In the case below a mean line is added. Other statistics can be added with similar code, just change the function fun=mean to the relevant function.

library(ggplot2)

HD1 <- iris[51:150, 4:5]
names(HD1) <- c("HT","LOCATION")
brks <- unique(HD1[[2]])

ggplot(data = HD1, aes(x = LOCATION, y = HT, fill = LOCATION)) + 
  geom_boxplot(notch = TRUE) +
  scale_fill_manual(breaks = brks, values = c("sky blue", "red")) +
  stat_summary(aes(ymax = ..y.., ymin = ..y..),
               geom = "errorbar", fun = mean,
               width = 0.70,
               size = 1.5, linetype = "dotted") +
  theme_bw() + 
  theme(panel.grid.major = element_blank(), 
        panel.grid.minor = element_blank())

Created on 2022-06-13 by the reprex package (v2.0.1)

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