Bug in by() with dates as levels?

hadley wickham <h.wickham <at> gmail.com> writes:

You might also want to take a look at the plyr package:

install.packages("plyr")
library(plyr)
ddply(x, .(A, D), function(df) sum(df$Z))
dlply(x, .(A, D), function(df) sum(df$Z))

I recently for the first time used the plyr package in an introductory 
course as a general replacement of for "by", "(x)apply", followed by 
do.call gymnastics. It was an amazing step forward to have a nicely 
orthogonal set of function that returns what people expected instead 
of converting everything to a list.

I know, real MEN program assembler and love (x)apply...


Dieter