How do I use `[` correctly with (l|s)apply to select a specific column from a list of matrices?

Question

Consider the following situation where I have a list of n matrices (this is just dummy data in the example below) in the object myList

mat <- matrix(1:12, ncol = 3) myList <- list(mat1 = mat, mat2 = mat, mat3 = mat, mat4 = mat) 

I want to select a specific column from each of the matrices and do something with it. This will get me the first column of each matrix and return it as a matrix (lapply() would give me a list either is fine).

sapply(myList, function(x) x[, 1]) 

What I can't seem able to do is use [ directly as a function in my sapply() or lapply() incantations. ?'[' tells me that I need to supply argument j as the column identifier. So what am I doing wrong that this does't work?

> lapply(myList, `[`, j = 1) $mat1 [1] 1  $mat2 [1] 1  $mat3 [1] 1  $mat4 [1] 1 

Where I would expect this:

$mat1 [1] 1 2 3 4  $mat2 [1] 1 2 3 4  $mat3 [1] 1 2 3 4  $mat4 [1] 1 2 3 4 

I suspect I am getting the wrong [ method but I can't work out why? Thoughts?

Answer 1

I think you are getting the 1 argument form of [. If you do lapply(myList, `[`, i =, j = 1) it works.