Index matrix with randomly sampled columns - r

Question

I'm trying to fill the columns of an index matrix with samples from 1:whatever using a for loop. The purpose of this is for a bootstrap coding problem. The issue I'm getting is that the for loop wont run correctly once it reaches a number that is not a multiple of the row length. For some reason it thinks I want an equal representation of number in each column. How do I get this to stop?
index.mat=matrix(NA,nr=12,nc=10,byrow=FALSE)
for(i in 1:5)
{
index.mat[,i] <- sample(1:i, i, replace=TRUE)
print(index.mat)
}
will print
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 1 1 2 1 NA NA NA NA NA NA
[2,] 1 1 2 4 NA NA NA NA NA NA
[3,] 1 1 2 1 NA NA NA NA NA NA
[4,] 1 1 2 2 NA NA NA NA NA NA
[5,] 1 1 2 1 NA NA NA NA NA NA
[6,] 1 1 2 4 NA NA NA NA NA NA
[7,] 1 1 2 1 NA NA NA NA NA NA
[8,] 1 1 2 2 NA NA NA NA NA NA
[9,] 1 1 2 1 NA NA NA NA NA NA
[10,] 1 1 2 4 NA NA NA NA NA NA
[11,] 1 1 2 1 NA NA NA NA NA NA
[12,] 1 1 2 2 NA NA NA NA NA NA
as the final matrix before giving the error
Error in index.mat[, i] <- sample(1:i, i, replace = TRUE) :
number of items to replace is not a multiple of replacement length

Answer 1

Just use sample(i, size = 12, replace = TRUE).
Your LHS is index.mat[,i] which has length 12.
Your RHS is sample(1:i, i, replace = TRUE), which has length i.
By nature, R will recycle the RHS when the lengths don't match up -- this means, when i=2, your RHS is length 2 and it will simply be repeated 6 times to match the LHS length 12.
In this particular case, if the RHS length isn't a divisor of the LHS length, you get an error -- which happens first when, you guessed it, i=5 (since 1, 2, 3, and 4 all divide 12 evenly).