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

Answer 1

The shared reproducible example suggests that you have the columns as factors. We need to convert them to numeric first.

We can try with base R ave. Finding out the max in each group.

x$max.per.group <- ave(x$replicate, x$group, FUN = function(x) max(as.numeric(x)))

#   group replicate max.per.group
#1      A         1             5
#2      A         2             5
#3      A         3             5
#4      A         4             5
#5      A         5             5
#6      B         1             2
#7      B         2             2
#8      C         1             3
#9      C         2             3
#10     C         3             3

---

Another option with dplyr

library(dplyr)
x %>%
   group_by(group) %>%
   mutate(max.per.group = max(as.numeric(replicate)))