I have two lists, each one with many matrices. For brevity, here is an example with two matrices per list:
l1 <- list(matrix(1:20, nrow=2),
matrix(21:40, nrow=2))
l2 <- list(matrix(41:60, nrow=2),
matrix(61:80, nrow=2))
I am trying to use lapply to (a) remove the first column of each matrix and then (b) multiply each matrix in l1 against the corresponding matrix in l2.
First, I tried:
result <- lapply(l1, function(x,y){
tmp <- x[,-1]*y[,-1]
return(tmp)
}, y=l2)
It didn't work. The problem is that I can't remove the first column from l2 this way. If l2 were a vector instead of a list, the code would work with tmp <- x[,-1]*y[-1]. But even when I try to simply multiply the matrices in each list, it still does not work:
result <- lapply(l1, function(x,y){
tmp <- x*y
return(tmp)
}, y=l2)
Any ideas?
In lapply, you can iterate over only one object. You may use Map here -
Map(function(x, y) x[,-1]*y[,-1], l1, l2)
#[[1]]
# [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#[1,] 129 225 329 441 561 689 825 969 1121
#[2,] 176 276 384 500 624 756 896 1044 1200
#[[2]]
# [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#[1,] 1449 1625 1809 2001 2201 2409 2625 2849 3081
#[2,] 1536 1716 1904 2100 2304 2516 2736 2964 3200
To use lapply you may use the index to subset both l1 and l2.
lapply(seq_along(l1), function(x) l1[[x]][, -1] * l2[[x]][, -1])