r - Create a list of multiple matrices with list instead of using a for loop

Question

I am working with a precipitation data set that is organised in an array (dimensions are 150 150 80). The third dimension respresents the single time steps. Additonally I have a matrix called "mask" of dimensions 150 150. The goal is to multiply this matrix with every single time step so that at the end there are 80 (which is equal to ntime) resulting matrices.

This can easily be done using a loop:

for (i in 1:ntime) {
  assign(paste0("matrix_out",i), PRECIPITATION[,,i]*mask)
}

The thing is that afterwards I have to deal with 80 matrices, called "matrix_out1, matrix_out1, ..., matrix_out80". It is possible to further process these data, but not very elegant though.

I am sure that there is a more handy way by using a list instead of creating 80 single objects. So far I am not so familiar with working with lists.

Does anybody can give me a hint how to do that?

question from:https://stackoverflow.com/questions/65936468/create-a-list-of-multiple-matrices-with-list-instead-of-using-a-for-loop

Answer 1

The simplest solution would be to add each loop result to a list:

matlist <- list()
for (i in 1:ntime) {
  matlist[[i]] = assign(paste0("matrix_out",i), PRECIPITATION[,,i]*mask)
}

Right, I forgot about the matrices saved to the environment. You can eliminate that with:

matlist <- list()
for (i in 1:ntime) {
  matlist[[i]] = PRECIPITATION[,,i]*mask
  names(matlist)[i] = paste0("matrix_out",i)
}

So the stand-alone matrices are not created