Why do i get “position_dodge requires constant width” even though widths are constant in ggplot2

Question

I\'m getting a warning message I don\'t understand for simple bar charts in ggplot2

> df <- data.frame(X = 127:131, Y = rnorm(5))
> df
    X          Y
         


        

Answer 1

Setting options(warn = 2, error = recover), and rerunning the code lets us find the problem.

Inside the collide function (number 16 in the call stack), there is this piece of code:

if (!zero_range(range(widths))) {
    warning(name, " requires constant width: output may be incorrect", 
        call. = FALSE)
}

Floating point rounding errors mean that widths takes slightly different values.

format(widths, digits = 22)
# [1] "0.9000000000000056843419" "0.8999999999999914734872" "0.8999999999999772626325"

The tolerance for checking that the numbers are the same is too strict: about 2.2e-14.

args(zero_range)
# function (x, tol = .Machine$double.eps * 100) 
# NULL
.Machine$double.eps * 100
# [1] 2.220446e-14

So the warning is erroneous; don't worry about it.