apply-on-nonnumeric-columns

[noamross]

https://github.com/noamross/zero-dependency-problems/blob/master/R/apply-on-nonnumeric-columns.md

I'm having some trouble applying things to a subset of the dataframe I'm using.

Diet121 <- subset(ChickWeight, Diet == 1 & Time == 21)

This works fine, and gives the subset I want, but when I try to apply the mean to the columns, I get an error message

apply(Diet121, 2, mean)
weight Time Chick Diet
NA NA NA NA
Warning messages:
1: In mean.default(newX[, i], ...) :
argument is not numeric or logical: returning NA
2: In mean.default(newX[, i], ...) :
argument is not numeric or logical: returning NA
3: In mean.default(newX[, i], ...) :
argument is not numeric or logical: returning NA
4: In mean.default(newX[, i], ...) :
argument is not numeric or logical: returning NA

I'm assuming I'm doing something stupid such as not attaching something correctly. Is something wrong with 'mean'?