Check whether string is contained within a list

Question

I'm trying to find a way to check whether a list contains an element that itself contains a particular string. Finding an exact match is simple with %in%:

list1 <- list("a","b","c")
"a" %in% list1
[1] TRUE

But it only works if the element is identical, i.e. it doesn't return TRUE if the element only contains the string:

list2 <- list("a,b","c,d")
"a" %in% list2
[2] FALSE

Is there a way to generate TRUE for the second example? Thanks in advance.

Something like `any(grepl("a", unlist(list2)))` ? Or if they are always comma separated then `"a" %in% unlist(strsplit(as.character(list2), ","))` — Ronak Shah, Dec 01 '17 at 01:23
commenting on @ronak-shah 's answer, if every element in `list2` is just a simple character string, `unlist()` can be omitted. `any(grepl("a",list2))` should do. — Yue Y, Dec 01 '17 at 01:36
I don't know anything about r. But I did find this thread: https://stackoverflow.com/questions/30180281/how-can-i-check-if-multiple-strings-exist-in-another-string — John Mitchell, Dec 01 '17 at 01:47
If you can use `c` instead of `list`, this question is simpler. — alistaire, Dec 01 '17 at 01:57

score 2 · Answer 1 · edited Dec 01 '17 at 05:24

2

Could you try flipping it around and using

any(list2 %like% 'a')

The any() is included because without it the output is : [1] TRUE FALSE

edited Dec 01 '17 at 05:24

Joseph Wood

6,489
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28
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answered Dec 01 '17 at 01:35

brett

131
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What package is `%like%` from? I haven't seen that one. – Marius Dec 01 '17 at 01:54
For some reason I thought it was a base function. But it isn't. It's in data.table – brett Dec 01 '17 at 01:58
@Marius `%like%` is in `library(data.table)` – user2256085 Jan 23 '22 at 03:00

score 1 · Answer 2 · answered Dec 01 '17 at 02:19

library(stringi)

list2 <- list("a,b","c,d")

stri_detect_fixed(list2, "a")
## [1]  TRUE FALSE

stri_detect_fixed(list2, "b")
## [1]  TRUE FALSE

stri_detect_fixed(list2, "c")
## [1] FALSE  TRUE

stri_detect_fixed(list2, "d")
## [1] FALSE  TRUE

stri_detect_fixed(list2, "q")
## [1] FALSE FALSE

Check whether string is contained within a list

2 Answers2