Set Operations in R

R can perform different operations in sets, such as union, intersection, asymmetric difference of two sets, etc. Specifically, the following operations are available in R for set operations.

Operator	Usage	Definition
union	union(x, y)	Union of sets x and y
intersect	intersect(x, y)	Intersection of sets x and y
setdiff	setdiff(x, y)	Asymmetric difference between sets x and y (Elements in x but not in y)
setequal	setequal(x, y)	If sets x and y have the same elements
is.element	is.element(el, set)	If el is an element of set

Examples:

> x <- c(sort(sample(1:20, 9)),NA)

> y <- c(sort(sample(3:23, 7)),NA)

> x

[1]  1  3  5  8 11 17 18 19 20 NA

> y

[1]  7 11 15 16 17 19 22 NA

> union(x, y)

[1]  1  3  5  8 11 17 18 19 20 NA  7 15 16 22

> intersect(x, y)

[1] 11 17 19 NA
> setdiff(x, y)

[1]  1  3  5  8 18 20

> setdiff(y, x)

[1]  7 15 16 22

> setequal(x, y)

[1] FALSE

Note that each of union, intersect, setdiff and setequal will discard any duplicated values in the arguments. Look at the following example:

> x

[1]  1  3  5  8 11 17 18 19 20 NA

> x2 <- c(x, 1, 3, 5, 8)

> x2

[1]  1  3  5  8 11 17 18 19 20 NA  1  3  5  8

> setdiff(x, y)

[1]  1  3  5  8 18 20

> setdiff(x2, y)

[1]  1  3  5  8 18 20

> setequal(x, x2)

[1] TRUE

Although x and x2 have different length, they have the same UNIQUE elements so setequal(x, x2) returns a TRUE value.

is.element(x, y) is identical to x %in% y which is already discussed here. The return value of is.element is a vector of TRUE and FALSE with the same length as x, which indicates whether each element of x is an element of y or not.

> is.element(x, y)  # vector of length 10

[1] FALSE FALSE FALSE FALSE  TRUE  TRUE FALSE  TRUE FALSE  TRUE

> is.element(y, x)  # vector of length 8

[1] FALSE  TRUE FALSE FALSE  TRUE  TRUE FALSE  TRUE