I have two matrices:
mat <- matrix(1:6, 2, 3)
mat2 <- matrix(1:2, 2, 3)
a <- 1
mat.new <- ifelse(a == 1, mat, mat2)
The length of the return is completely decided by
length(a == 1). See also the helpfile with
?ifelse. Your code will only return a single value.
ifelse targets vector input / output. Even if you get the length correct, say:
ifelse(rep(TRUE, 6), mat, mat2), you get a vector rather than a matrix output. So an outer
matrix call to reset dimension is necessary.
For your example, looks like a simple
result <- if (a == 1) mat else mat2 is sufficient. No need to touch
It is not impossible to ask
ifelse to return a matrix, but you have to protect it by a list (remember a list is a vector):
ifelse(TRUE, list(mat), list(mat2))
But, this is inconvenient.