generate column values with multiple conditions in R

Question

I have a dataframe z and I want to create the new column based on the values of two old columns of z. Following is the process:

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Answer 1

Based on the suggestion of Señor :

> z$q <- ifelse(z$x == 2, z$t * 2,
         ifelse(z$x == 4, z$t * 4,
         ifelse(z$x == 7, z$t * 3,
                          z$t * 1)))
> z
    x  y  t  q
1   1 11 21 21
2   2 12 22 44
3   3 13 23 23
4   4 14 24 96
5   5 15 25 25
6   6 16 26 26
7   7 17 27 81
8   8 18 28 28
9   9 19 29 29
10 10 20 30 30