How to add value of mean in number in violin plot using base R

Question

I have data

Name    V1
M1      50 
M2      10 
M1      30
M1      45
M2      5
M2      7

With my code, I was able to produce a violin plot. But I don't know how to put the value of mean in each violin plot in number using base R (not ggplot)?

Here is an example of my code.

with(Data, vioplot(V1[Name=="M1"], V1[Name=="M2"], names=c("M1", "M2"), 
                   plotCentre="line", rectCol="white", col="gray", ylab="", 
                   ylim=c(0,80)))
title(ylab="A($m)", xlab="Name", main="AA")

Thanks a lot

Answer 1

You could use the following code:

Your data:

Data <- read.table(header = TRUE, 
            text = "Name    V1
                    M1      50 
                    M2      10 
                    M1      30
                    M1      45
                    M2      5
                    M2      7")

Code

library(vioplot)
library(dplyr)

## calculate the mean per group
DataMean <- Data %>% 
  group_by(Name) %>%
  summarize(mean = mean(V1))

## your plotting code
with(Data, vioplot(V1[Name=="M1"], V1[Name=="M2"], names=c("M1", "M2"), 
                   plotCentre="line", rectCol="white", col="gray", ylab="", 
                   ylim=c(0,80)))
title(ylab="A($m)", xlab="Name", main="AA")

## use base r 'text' to add the calculated means
## at position 1 and 2 on the X-axis, and
## at height of the Y-axis of 60 (2 times)
text(x = c(1, 2), y = c(60,60), labels = round(DataMean$mean, 2))

yielding the following plot:

Of course, we can play around with the position of the text. If we want the means to appear inside the violin plots, we use the mean values as Y-coordinates, and change the color to make it more visible (and shift the X-coordinates a little to the right, in combination with a lighter grey).

### playing with position and color
with(Data, vioplot(V1[Name=="M1"], V1[Name=="M2"], names=c("M1", "M2"), 
                   plotCentre="line", rectCol="white", col="lightgray", ylab="", 
                   ylim=c(0,80)))
title(ylab="A($m)", xlab="Name", main="AA")
text(x = c(1.1, 2.1), y = DataMean$mean, labels = round(DataMean$mean, 2), col = "blue")

yielding this plot:

Please, let me know whether this is what you want.