Remove empty elements from list with character(0)
RListR Problem Overview
How can I remove empty elements from a list that contain zero length pairlist as
character(0), integer(0) etc...
list2
# $`hsa:7476`
# [1] "1","2","3"
#
# $`hsa:656`
# character(0)
#
# $`hsa:7475`
# character(0)
#
# $`hsa:7472`
# character(0)
I don't know how to deal with them. I mean if NULL it is much simpler. How can I remove these elements such that just hsa:7476 remains in the list.
R Solutions
Solution 1 - R
Another option(I think more efficient) by keeping index where element length > 0 :
l[lapply(l,length)>0] ## you can use sapply,rapply
[[1]]
[1] 1 2 3
[[2]]
[1] "foo"
Solution 2 - R
One possible approach is
Filter(length, l)
# [[1]]
# [1] 1 2 3
#
# [[2]]
# [1] "foo"
where
l <- list(1:3, "foo", character(0), integer(0))
This works due to the fact that positive integers get coerced to TRUE by Filter and, hence, are kept, while zero doesn't:
as.logical(0:2)
# [1] FALSE TRUE TRUE
Solution 3 - R
For the sake of completeness, the purrr package from the popular tidyverse has some useful functions for working with lists - compact (introduction) does the trick, too, and works fine with magrittr's %>% pipes:
l <- list(1:3, "foo", character(0), integer(0))
library(purrr)
compact(l)
# [[1]]
# [1] 1 2 3
#
# [[2]]
# [1] "foo"
or
list(1:3, "foo", character(0), integer(0)) %>% compact
Solution 4 - R
Funny enough, none of the many solutions above remove the empty/blank character string: "". But the trivial solution is not easily found: L[L != ""].
To summarize, here are some various ways to remove unwanted items from an array list.
# Our Example List:
L <- list(1:3, "foo", "", character(0), integer(0))
# 1. Using the *purrr* package:
library(purrr)
compact(L)
# 2. Using the *Filter* function:
Filter(length, L)
# 3. Using *lengths* in a sub-array specification:
L[lengths(L) > 0]
# 4. Using *lapply* (with *length*) in a sub-array specification:
L[lapply(L,length)>0]
# 5. Using a sub-array specification:
L[L != ""]
# 6. Combine (3) & (5)
L[lengths(L) > 0 & L != ""]
Solution 5 - R
Use lengths() to define lengths of the list elements:
l <- list(1:3, "foo", character(0), integer(0))
l[lengths(l) > 0L]
#> [[1]]
#> [1] 1 2 3
#>
#> [[2]]
#> [1] "foo"
#>