Split a list whose elements are multiple element lists

Question

Say I have a list a which is defined as:

a <- list("aaa;bbb", "aaa", "bbb", "aaa;ccc")

I want to split this list by semicolon ;, get only unique values, and return another list. So far I have split the list using str_split():

a <- str_split(a, ";")

which gives me

> a
[[1]]
[1] "aaa" "bbb"

[[2]]
[1] "aaa"

[[3]]
[1] "bbb"

[[4]]
[1] "aaa" "ccc"

How can I manipulate this list (using unique()?) to give me something like

[[1]]
[1] "aaa" 

[[2]]
[1] "bbb"

[[3]]
[1] "ccc"

or more simply,

[[1]]
[1] "aaa" "bbb" "ccc"

Hey @Sotos can you please submit this as an answer so I can accept? This works wonderfully. — Kyle Weise, Jul 24 '17 at 13:10
Actually, this returns a result of class character when I need a list. — Kyle Weise, Jul 24 '17 at 13:14

Miha · Accepted Answer · 2017-07-24T13:13:46.223

3

One option is to use list() with unique() and unlist() inside your list.

    # So first you use your code
    a <- list("aaa;bbb", "aaa", "bbb", "aaa;ccc")
    # Load required library 
    library(stringr) # load str_split
    a <- str_split(a, ";")
    # Finally use list() with unique() and unlist()
    list(unique(unlist(a)))
    # And the otuput
    [[1]]
    [1] "aaa" "bbb" "ccc"

edited Jul 24 '17 at 13:13

answered Jul 24 '17 at 13:03

Miha

2,559
2
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3

you could use `strsplit(unlist(a))`, which works with `strsplit` from base R (no real need for `library(stringr)` – Ben Bolker Jul 24 '17 at 13:15
@Miha we have an "Rkoholiki" slack going on. Drop me a line at romunov located at gmail if you would like to join us. This message will self destruct in XY minutes. :) – Roman Luštrik Jul 24 '17 at 14:18

lmo · Answer 2 · 2017-07-24T13:19:10.867

3

One alternative in base R is to use rapply which applies a function to each of the inner most elements in a nested list and returns the most simplified object possible by default. Here, it returns a vector of characters.

unique(rapply(a, strsplit, split=";"))
[1] "aaa" "bbb" "ccc"

To return a list, wrap the output in list

list(unique(rapply(a, strsplit, split=";")))
[[1]]
[1] "aaa" "bbb" "ccc"

edited Jul 24 '17 at 13:19

answered Jul 24 '17 at 13:16

lmo

37,904
9
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Split a list whose elements are multiple element lists

2 Answers2