Conditionally remove NULL elements of a list

Question

Let´s say I have a list in R:

a <- c(1,2,3)
f <- NULL
b <- c("a","b","c")
d <- list(a,f,b)

yielding

> d
[[1]]
[1] 1 2 3

[[2]]
NULL

[[3]]
[1] "a" "b" "c"

I know it sounds dumb to build a list like this, but I get this from a previous computation (I could have set f to be 0 or any other character). I tried to remove f since I need the algorithm to perform operations in valid columns a and b, but unsuccessfully so far. d[2] is still there...

So how do I remove d[2] from the list? It should go from length = 3 to length = 2, and in the real instance I don´t know beforehand which elements of the list are NULL, so an if-based response would be great...

Cheers,

@MauritsEvers oops you are right...I missed that question. Great answer, btw, really solves the issue, thanks. — Arrebimbomalho, Mar 05 '18 at 01:24

score 1 · Answer 1 · answered Mar 05 '18 at 01:20

1

use the is.null function from R to identify which elements are NULL. This will work:

d[-which(lapply(d,is.null) == T)]

answered Mar 05 '18 at 01:20

Alejandro Andrade

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Are you sure? Will have to try tomorrow, but That seems to be for a dataframe...cheers – Arrebimbomalho Mar 05 '18 at 01:23
2

`lapply` is for list that's why it has l before apply. Also if you look at the `Filter` source code is basically a wrapper of my answer – Alejandro Andrade Mar 05 '18 at 01:27
@Arrebimbomalho ... also a `data.frame` is really nothing else but a `list` with [some restrictions](https://stackoverflow.com/a/15902963/6530970) – Maurits Evers Mar 05 '18 at 01:30
@AlejandroAndrade Fair enough. Still wrapping my head (pun intended) around the apply family of functions...Thanks, man! – Arrebimbomalho Mar 05 '18 at 01:32

Conditionally remove NULL elements of a list

1 Answers1