[SOLVED] Error when using the apply function on a matrix in R

Error when using the apply function on a matrix in R

I'm trying to use apply to use the L1 norm on each column of a matrix in R. If we have a matrix

X=matrix(data=rnorm(100),nrow=10,ncol=10)

Then when I run

apply(X,2,function(x) norm(x,type="1"))

I get the error:

Error in base::norm(x, type, ...) : 'A' must be a numeric matrix

I've found that this is because when we index X, we lose the matrix type. For example, running

norm(X[,1],type="1")

we get the same error. Hence, I've run

  old <- `[`
`[` <- function(...) { old(..., drop=FALSE) }

To stop the matrix type being dropped when we subset X. Now, this works

norm(X[,1],type="1")

But I still get the same error for

apply(X,2,function(x) norm(x,type="1"))

Solution

You could do apply(X, 2, function(x) norm(matrix(x, ncol = 1), type = "1"), but you could also just do colSums(abs(X))--there's not much point in using norm here.