unlist to produce a vector of same length

Question

I have a list like this:

lst <- list(a = c("y"), b = c("A", "B", "C"), c = c("x1", "x2"))
lst

> lst
$a
[1] "y"

$b
[1] "A" "B" "C"

$c
[1] "x1" "x2"

If I unlist it, I get:

unlist(lst)
> unlist(lst)
   a   b1   b2   b3   c1   c2 
 "y"  "A"  "B"  "C" "x1" "x2"

How can I get a vector like:

        a         b         c 
      "y" "A, B, C"  "x1, x2"

Edit: A similar question Convert a list of lists to a character vector was answered previously. The answer proposed by @42_ sapply( l, paste0, collapse="") could be used with a small modification: sapply( l, paste0, collapse=", "). Ronak Shah's sapply(lst, toString) to my question is a little more intuitive.

Possible duplicate of [Convert a list of lists to a character vector](https://stackoverflow.com/questions/34624289/convert-a-list-of-lists-to-a-character-vector) — camille, Oct 04 '19 at 02:05
Thanks. This is slightly different from the previous question. A small modification of those answers would solve my problem. The solution `sapply(lst, toString)` by Ronak Shah is simpler than previous answers. — Zhiqiang Wang, Oct 04 '19 at 02:26
A separator of `""` and one of `", "` don't seem substantially different — camille, Oct 04 '19 at 03:07
For new R users, it is difficult to get our heads around functions like `apply` and `paste`. A smallest difference may take a long time to work out. Ronak Shah's solution directly answers my question, simple and straightforward. I have learned something new and useful from this answer which could also help others. — Zhiqiang Wang, Oct 04 '19 at 03:42

score 2 · Accepted Answer · answered Oct 04 '19 at 01:56

We can use toString to collapse all the elements in every list into a comma-separated string.

sapply(lst, toString)
#     a       b       c 
#    "y" "A,B,C" "x1,x2"

which is same as using paste with collapse argument as ","

sapply(lst, paste, collapse = ",")

yusuzech · Answer 2 · 2019-10-04T02:12:42.287

1

You can also do

unlist(Map(function(x) paste0(x,collapse = ","),lst))

Or

unlist(lapply(lst,function(x) paste0(x,collapse = ",")))

Or use purrr package

purrr::map_chr(lst,paste0,collapse = ",")

edited Oct 04 '19 at 02:12

answered Oct 04 '19 at 02:02

yusuzech

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score 1 · Answer 3 · answered Oct 04 '19 at 16:34

1

we can use map

library(purrr)
library(stringr)
map_chr(lst, str_c, collapse=",")

answered Oct 04 '19 at 16:34

akrun

874,273
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unlist to produce a vector of same length

3 Answers3