Test if a vector contains a given element

573
votes

How to check if a vector contains a given value?

7
rvectorr-faq
sometimes I ask myself why R just doesn't use the word contains to make it users easier – greg121
consider that "in" is contained in "conta(in)s"; I'd contend that "in" is a considerably concise contender in this context – hedgedandlevered
Perhaps with the addition of flanking %-signs that is. The word in is a reserved word in R use in for-loop construction. – IRTFM
@greg121 dplyr already has a contains 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
Is there a concise way to do it for real valued numbers with a given precision? – mlt

7 Answers

545
votes

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
191
votes

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
91
votes

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

71
votes

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
37
votes

You can use the %in% operator:

vec <- c(1, 2, 3, 4, 5)
1 %in% vec # true
10 %in% vec # false
20
votes

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))]
13
votes

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.