[R] functions on rows or columns of two (or more) arrays

[Florent D.]

The apply function also works with multi-dimensional arrays, I think
this is what you want to achieve using a 3d array:

aaa <- array(NA, dim = c(2, dim(a)))
aaa[1,,] <- a
aaa[2,,] <- a2
apply(aaa, 3, function(x)lm(x[1,]~x[2,]))