Test if a vector contains a given element
RVectorR FaqR Problem Overview
How to check if a vector contains a given value?
R Solutions
Solution 1 - R
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
Solution 2 - R
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
Solution 3 - R
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
Solution 4 - R
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
Solution 5 - R
You can use the %in% operator:
vec <- c(1, 2, 3, 4, 5)
1 %in% vec # true
10 %in% vec # false
Solution 6 - R
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))]
Solution 7 - R
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.