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rdataframecumsummultiple-conditions

R- Include starting point in cumsum function

I have this data.frame:

       a b
 [1,]  1 0
 [2,]  2 0
 [3,]  3 0
 [4,]  4 0
 [5,]  5 0
 [6,]  6 1
 [7,]  7 2
 [8,]  8 3
 [9,]  9 4
[10,] 10 5

I want to apply cumsum on column a only when its corresponding value on column b is different from 0.

I tried this below but it doesn't include a starting condition on the cumsum:

   df_cumsum <- cbind(c(1:10), c(0,0,0,0,0,1,2,3,4,5),
                       as.data.frame(ave(A[,1], A[,2] != 0, FUN=cumsum)))

Unfortunately, I obtain a cumsum over the whole column:

    a b  c
1   1 0  1
2   2 0  3
3   3 0  6
4   4 0 10
5   5 0 15
6   6 1  6
7   7 2 13
8   8 3 21
9   9 4 30
10 10 5 40

I would like to obtain:

    a b  c
1   1 0  0
2   2 0  0
3   3 0  0
4   4 0  0
5   5 0  0
6   6 1  6
7   7 2 13
8   8 3 21
9   9 4 30
10 10 5 40

Thanks for help!

Solution

  • It would be better to create an index and update

    i1 <- df1$b > 0
df1$c[i1] <- with(df1, cumsum(a[i1]))

    Or in a single line

    df1$c <- with(df1, cumsum(a * (b > 0)))
df1$c
#[1]  0  0  0  0  0  6 13 21 30 40