my matrix is:

d1

a b

[1,] 1 2

[2,] 2 2

[3,] 4 1

If I do the following I got the result:

rep(1,d1[1,2])

[1] 1 1

rep(1,d1[2,2])

[1] 1 1

rep(1,d1[3,2])

[1] 1

But why getting invalid 'times' argument for the following:

j=c(1:3)

j

[1] 1 2 3

rep(1,d1[j,2])

Error in rep(1, d1[j, 2]) : invalid 'times' argument