Test if a vector contains a given element

Question

How to check if a vector contains a given value?

sometimes I ask myself why R just doesn't use the word contains to make it users easier — greg121, Mar 04 '13 at 17:28
consider that "in" is contained in "conta(in)s"; I'd contend that "in" is a considerably concise contender in this context — hedgedandlevered, Mar 11 '16 at 16:34
Perhaps with the addition of flanking `%`-signs that is. The word `in` is a reserved word in R use in for-loop construction. — IRTFM, Jul 09 '16 at 00:44
@greg121 dplyr already has a [contains](http://dplyr.tidyverse.org/reference/select_helpers.html) function, but it's used for a different purpose: to select a column in a data frame. For example `select(iris, contains("etal"))`. — Paul Rougieux, Mar 14 '18 at 09:59
Is there a concise way to do it for real valued numbers with a given precision? — mlt, Nov 16 '18 at 19:45
@greg121 `in` also exist in popular languages such as JavaScript, Python and SQL, so not sure what so special about in R in particular- I would even bet R creators took it from one of them. — David Arenburg, Aug 07 '19 at 17:14

score 600 · Accepted Answer · edited Apr 27 '11 at 18:15

600

Both the match() (returns the first appearance) and %in% (returns a Boolean) functions are designed for this.

v <- c('a','b','c','e')

'b' %in% v
## returns TRUE

match('b',v)
## returns the first location of 'b', in this case: 2

edited Apr 27 '11 at 18:15

Community

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answered Jul 23 '09 at 02:25

medriscoll

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what about getting all appearances, not just the first one? – StatsSorceress Mar 15 '18 at 00:54
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Maybe I come a little late. `which(v, 'b')`. Mind the order of the arguments. – Niklas Mertsch Dec 19 '18 at 19:40
Your `which(v, 'b')` gives me an error message: >Error in which(v, 'b') : argument to 'which' is not logical – Capt.Krusty Aug 17 '19 at 10:08
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The syntax is which(v == b) or any other logical operator. In this case, the return from this would be 2. If v were c("b", "b", "c", "b", "d"), the return to which(v == b) would be 1, 2, 4. – khtad Jun 26 '20 at 21:33

score 203 · Answer 2 · answered Oct 02 '13 at 12:03

203

is.element() makes for more readable code, and is identical to %in%

v <- c('a','b','c','e')

is.element('b', v)
'b' %in% v
## both return TRUE

is.element('f', v)
'f' %in% v
## both return FALSE

subv <- c('a', 'f')
subv %in% v
## returns a vector TRUE FALSE
is.element(subv, v)
## returns a vector TRUE FALSE

answered Oct 02 '13 at 12:03

Justin Nafe

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I know the documentation says `is.element(x, y) is identical to x %in% y`. But, I dont know why, `is.elements` works when mixing integers and numerics and `%in%` doesn't – pomber Dec 28 '14 at 06:21
@pomber : Could you give an example of this? – discipulus Jun 27 '17 at 06:24
@pomber is it fixed? – vasili111 Sep 21 '19 at 23:28
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The superior readability `is.element()` vs `%in%` is subjective. A case can be made that an infix operator is more readable because it eliminates ambiguity in the order of arguments. `apple in fruit` makes sense, `fruit in apple` does not. `is.element(apple, fruit)` or `is.element(fruit, apple)` could both be right depending on implementation of the `is.element` function. – rileymcdowell Jan 03 '20 at 16:36

ishandutta2007 · Answer 3 · 2017-07-18T02:54:05.343

120

I will group the options based on output. Assume the following vector for all the examples.

v <- c('z', 'a','b','a','e')

For checking presence:

%in%

> 'a' %in% v
[1] TRUE

any()

> any('a'==v)
[1] TRUE

is.element()

> is.element('a', v)
[1] TRUE

For finding first occurance:

match()

> match('a', v)
[1] 2

For finding all occurances as vector of indices:

which()

> which('a' == v)
[1] 2 4

For finding all occurances as logical vector:

==

> 'a' == v
[1] FALSE  TRUE FALSE  TRUE FALSE

Edit: Removing grep() and grepl() from the list for reason mentioned in comments

edited Jul 18 '17 at 02:54

answered Jun 07 '17 at 12:52

ishandutta2007

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As already commented [here](https://stackoverflow.com/questions/1169248/r-function-for-testing-if-a-vector-contains-a-given-element/34056066#comment66181358_34056066) and [here](https://stackoverflow.com/questions/1169248/r-function-for-testing-if-a-vector-contains-a-given-element/34056066#comment73025314_34056066), don't use `grep()` or regular expressions to find exact matches. – Uwe Jun 13 '17 at 10:04

score 71 · Answer 4 · answered Aug 20 '09 at 22:12

71

The any() function makes for readable code

> w <- c(1,2,3)
> any(w==1)
[1] TRUE

> v <- c('a','b','c')
> any(v=='b')
[1] TRUE

> any(v=='f')
[1] FALSE

answered Aug 20 '09 at 22:12

Dan Goldstein

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Be aware this behaves differently from `%in%`: `any(1==NA)` returns `NA`, where `1 %in% NA` returns `FALSE`. – Mar 23 '17 at 01:34
@user3603486: `any(1==NA, na.rm=TRUE)` returns `FALSE`. – AkselA Apr 23 '19 at 20:57

score 37 · Answer 5 · answered Jul 23 '09 at 02:25

37

You can use the %in% operator:

vec <- c(1, 2, 3, 4, 5)
1 %in% vec # true
10 %in% vec # false

answered Jul 23 '09 at 02:25

ars

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score 20 · Answer 6 · edited Jan 04 '22 at 03:59

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Also to find the position of the element "which" can be used as

pop <- c(3, 4, 5, 7, 13)

which(pop==13)

and to find the elements which are not contained in the target vector, one may do this:

pop <- c(1, 2, 4, 6, 10)

Tset <- c(2, 10, 7)   # Target set

pop[which(!(pop%in%Tset))]

edited Jan 04 '22 at 03:59

ah bon

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answered Aug 18 '13 at 01:12

Armin

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`which` is actually preferable sometimes for it gives you *all* the matching positions (as an array), unlike `match`. Although this was perhaps not what the OP asked for, unlike http://stackoverflow.com/questions/1169388/finding-multiple-elements-in-a-vector – Fizz Feb 07 '15 at 16:27
2

Why bother with `which` if you just want to find the elements not in `Tset`? You can just index `pop` directly; `pop[!pop%in%Tset]` – Houshalter Feb 20 '17 at 23:11

score 12 · Answer 7 · answered Dec 03 '15 at 01:02

12

I really like grep() and grepl() for this purpose.

grep() returns a vector of integers, which indicate where matches are.

yo <- c("a", "a", "b", "b", "c", "c")

grep("b", yo)
[1] 3 4

grepl() returns a logical vector, with "TRUE" at the location of matches.

yo <- c("a", "a", "b", "b", "c", "c")

grepl("b", yo)
[1] FALSE FALSE  TRUE  TRUE FALSE FALSE

These functions are case-sensitive.

answered Dec 03 '15 at 01:02

ojdajuiceman

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By default, `grep` takes a regular expression as its first element, so to do an exact match for `"b"`, either use`^e$` or add `, fixed=TRUE`). – reinierpost Jan 07 '16 at 07:45
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Do not use regex for exact matches. This is dangerous and can have unexpected results – David Arenburg Sep 10 '16 at 17:54
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Yeah, this is a terrible, no good, very bad idea - inefficient and guaranteed to break. E.g. `myvar <- 'blah'; grepl('b', myvar, fixed=TRUE)` will return `TRUE` even though 'b' is not in `myvar`. – Mar 23 '17 at 01:31

score 1 · Answer 8 · answered Jul 16 '22 at 18:43

Another option to check if a element exists in a vector is by using the %in{}% syntax from the inops package like this:

library(inops)
#> 
#> Attaching package: 'inops'
#> The following object is masked from 'package:base':
#> 
#>     <<-
v <- c('a','b','c','e')
v %in{}% c("b")
#> [1] FALSE  TRUE FALSE FALSE

^{Created on 2022-07-16 by the reprex package (v2.0.1)}

Test if a vector contains a given element

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