J Miller J Miller - 25 days ago 15
R Question

create a boxplot in R that labels a box with the sample size (N)

Is there a way to create a boxplot in R that will display with the box (somewhere) an "N=(sample size)"? The varwidth logical adjusts the width of the box on the basis of sample size, but that doesn't allow comparisons between different plots.

FWIW, I am using the boxplot command in the following fashion, where 'f1' is a factor:

boxplot(xvar ~ f1, data=frame, xlab="input values", horizontal=TRUE)

Answer

Here's some ggplot2 code. It's going to display the sample size at the sample mean, making the label multifunctional!

First, a simple function for fun.data

give.n <- function(x){
   return(c(y = mean(x), label = length(x)))
}

Now, to demonstrate with the diamonds data

ggplot(diamonds, aes(cut, price)) + 
   geom_boxplot() + 
   stat_summary(fun.data = give.n, geom = "text")

You may have to play with the text size to make it look good, but now you have a label for the sample size which also gives a sense of the skew.

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