In R, how do I add a max by group? [duplicate]

Answer 1

Here is an other base R solution:

cbind(x, cummax=unlist(tapply(x$replicate, x$group, function(x) rep(max(x), length(x)))))
   group replicate cummax
A1     A         1      5
A2     A         2      5
A3     A         3      5
A4     A         4      5
A5     A         5      5
B1     B         1      2
B2     B         2      2
C1     C         1      3
C2     C         2      3
C3     C         3      3