Cumsum with reset when 0 is encountered and by groups

Question

Below is my dataframe, I\'d like to get the \"yes\" column. I can\'t seem to get the cumsum to reset when it hits the 0 based on the \"value\" field by \"id\". Th

Answer 1

You can create a new by variable on the fly like this:

test[, wrong := cumsum(value), by=.(id, tempID=cumsum(value==0))]
test
    id value correct wrong
 1:  1     1       1     1
 2:  1     1       2     2
 3:  1     0       0     0
 4:  1     1       1     1
 5:  2     1       1     1
 6:  2     1       2     2
 7:  2     1       3     3
 8:  2     1       4     4
 9:  3     0       0     0
10:  3     1       1     1
11:  3     1       2     2
12:  3     0       0     0
13:  4     1       1     1
14:  4     1       2     2
15:  4     0       0     0
16:  4     0       0     0

Note that test <- is not necessary here, as := will update the data.table by reference.