Dear List,

I'll appreciate your help on this. I'm trying to create a variable as in
"cumsum_y.cond1" below, which should compute the cumulative sum of "y"
conditional on the value of cond==1.

set.seed(1)
d <- data.frame(y= sample(c(0,1), 10, replace= T),
                cond= sample(c(0,1), 10, replace= T))


   y cond  cumsum_y.cond1
 1  0    0     0
 2  0    0     0
 3  1    1     1
 4  1    0     1
 5  0    1     1
 6  1    0     1
 7  1    1     2
 8  1    1     3
 9  1    0     3
10 0    1     3

Thank you.

Regards,
Axel.

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