Hi,
I have a data.frame of the following type:
F = data.frame(read.table(textConnection(" A B
1 1 4
2 1 3
3 1 1
4 1 4
5 1 2
6 1 2
7 1 2
8 2 1
9 2 1
10 2 1
11 2 1
12 3 2
13 3 4
14 3 1
15 3 1
16 3 1"),head=TRUE,stringsAsFactors=FALSE))
F
A B
1 1 4
2 1 3
3 1 1
4 1 4
5 1 2
6 1 2
7 1 2
8 2 1
9 2 1
10 2 1
11 2 1
12 3 2
13 3 4
14 3 1
15 3 1
16 3 1
I want to generate a new column in which I calculate the (cum)sum of the
last 3 B's for each group A, so that F$C becomes:
A B C
1 1 4 0
2 1 3 4
3 1 1 7
4 1 4 8
5 1 2 8
6 1 2 7
7 1 2 8
8 2 1 0
9 2 1 1
10 2 1 2
11 2 1 3
12 3 2 0
13 3 4 2
14 3 1 6
15 3 1 7
16 3 1 6
I tried this:
library(zoo)
F$C = rollapply(as.zoo(F$B), 3, FUN = function(x) cumsum(x)-(x),na.pad=TRUE)
Thanks!
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