Extract non null elements from a list in R

Question

I have a list like this:

    x = list(a = 1:4, b = 3:10, c = NULL)
    x
    #$a
    #[1] 1 2 3 4
    #
    #$b
    #[1]  3  4  5  6  7  8  9 10
    #
    #$         


        

Answer 1

Simpler and likely quicker than the above, the following works for lists of any non-recursive (in the sense of is.recursive) values:

example_1_LST <- list(NULL, a=1.0, b=Matrix::Matrix(), c=NULL, d=4L)
example_2_LST <- as.list(unlist(example_1_LST, recursive=FALSE))

str(example_2_LST) prints:

List of 3
 $ a: num 1
 $ b:Formal class 'lsyMatrix' [package "Matrix"] with 5 slots
  .. ..@ x       : logi NA
  .. ..@ Dim     : int [1:2] 1 1
  .. ..@ Dimnames:List of 2
  .. .. ..$ : NULL
  .. .. ..$ : NULL
  .. ..@ uplo    : chr "U"
  .. ..@ factors : list()
 $ d: int 4