subset in a list

[Farm]

Hi fam,

I need to retrieve all items in paths list that have a length of 4.

e.g length(paths[[3]])
=4

[FJCC]

Here is one method.

paths <- list(c("A", "S", "D"), c("Z", "X", "C", "V"), c("W"),
              c("W", "E", "R", "T"))
LENGTHS <- sapply(paths,length)
paths[LENGTHS==4]
#> [[1]]
#> [1] "Z" "X" "C" "V"
#> 
#> [[2]]
#> [1] "W" "E" "R" "T"

^{Created on 2022-06-25 by the reprex package (v2.0.1)}

[amtrm]

R base has a Filter function for filtering lists and vectors.
With paths as it is defined in FJCC's post,

paths <- list(c("A", "S", "D"), c("Z", "X", "C", "V"), c("W"), c("W", "E", "R", "T"))
Filter(function(x) length(x) == 4, paths)

See ?Filter for details.

[michaelbgarcia]

And then there is keep from {purrr}

library(purrr)
paths <- list(c("A", "S", "D"), c("Z", "X", "C", "V"), c("W"), c("W", "E", "R", "T"))
keep(paths, ~length(.x) == 4)
#> [[1]]
#> [1] "Z" "X" "C" "V"
#> 
#> [[2]]
#> [1] "W" "E" "R" "T"

^{Created on 2022-06-29 by the reprex package (v2.0.1)}