Test if a vector contains a given element - r

Question

How to check if a vector contains a given value?

Answer 1

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

Answer 2

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

Answer 3

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

Answer 4

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

Answer 5

You can use the %in% operator:
vec <- c(1, 2, 3, 4, 5)
1 %in% vec # true
10 %in% vec # false

Answer 6

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))]

Answer 7

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.

Answer 8

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)