Outliers are missing when using plotrix boxplot() in R

Question

Instead of R's own boxplot() the outliers are missing when using gap.boxplot() from the plotrix package. I try to understand why.

See this example please:

> mtcars[2,c('mpg')] <- 45
> mtcars[6,c('mpg')] <- 77

Using boxplot(mtcars$mpg) you can see two extra dots (the outliers) on top of the boxplot.

Using gap.boxplot(mtcars$mpg) from plotrix package result in that graphic

The big question is why and how to solve this?

Answer 1

I have found a workaround to get the outliers. It involves accessing the value of outliers from the gap.boxplot command. Looks like the value of outliers are being computed but not plotted. I am curious to find out why it is happening.

gap.boxplot(mtcars$mpg)
outliers = gap.boxplot(mtcars$mpg)$out
points(x = rep(1,length(outliers)), y = c(outliers))