In R, how do I add a max by group? [duplicate]
I would like to use R to create a new column in my dataset that includes a maximum for each unique group. My data look like this:
group<-c("A","A","A","A","A","B","B","C","C","C")
replicate<-c(1,2,3,4,5,1,2,1,2,3)
x<-data.frame(cbind(group,replicate))
I'd like to create the third column as shown below - the maximum for each group.
group replicate max.per.group
A 1 5
A 2 5
A 3 5
A 4 5
A 5 5
B 1 2
B 2 2
C 1 3
C 2 3
C 3 3
If you redefine x first (the cbind makes both columns factors),
x<-data.frame(group,replicate)
you can use this:
merge(x,aggregate(replicate~group,x,FUN=max),all.x=TRUE,by="group")
group replicate.x replicate.y
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
Try
# This is how you create your data.frame
group<-c("A","A","A","A","A","B","B","C","C","C")
replicate<-c(1,2,3,4,5,1,2,1,2,3)
x<-data.frame(group,replicate) # here you don't need c()
# Here's my solution
Max <- tapply(x$replicate, x$group,max)
data.frame(x, max.per.group=rep(Max, table(x$group)))
group replicate max.per.group
1 A 1 5
2 A 2 5
3 A 3 5
4 A 4 5
5 A 5 5
6 B 1 2
7 B 2 2
8 C 1 3
9 C 2 3
10 C 3 3
Here is an other base R solution:
cbind(x, cummax=unlist(tapply(x$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