Efficient functional programming (using mapply) in R for a “naturally” procedural problem

Question

A common use case in R (at least for me) is identifying observations in a data frame that have some characteristic that depends on the values in some subset of other observa

Answer 1

This situation is tailor-made for using the plyr package.

ddply(raw, .(WorkerId), function(df) df[-NROW(df),])

It produces the output

WorkerId Iteration
1        1         1
2        1         2
3        1         3
4        2         1
5        2         2
6        2         3
7        3         1
8        3         2
9        3         3