Get All Pairs Out of One or Two Sets of Elements

Returns all combinations of 2 out of the elements in x or x and y (if defined). Combinations of the same elements will be dropped (no replacing). The vector x need not contain unique values. Duplicate elements in x will result in duplicate pairs.

Usage

combPairs(x, y = NULL)

Arguments

x

a vector of elements, must contain at least 2 elements if y is NULL.

y

a vector of elements, need not be same dimension as x. If y is not NULL then all combination x and y are returned.

Value

a data.frame with two columns X1 and X2 containing the pairwise combinations.

Details

If y = NULL then all combination of 2 out of x are returned.
If y is defined then all combinations of x and y are calculated.

See also

combn(), expand.grid(), outer(), lower.tri()

Other combinatorics: combN(), combSet(), pairApply(), permn(), randGroupSplit(), sampleX()

Examples

combPairs(letters[1:4])
#>   X1 X2
#> 1  a  b
#> 2  a  c
#> 3  a  d
#> 4  b  c
#> 5  b  d
#> 6  c  d
combPairs(x = letters[1:4], y = LETTERS[1:2])
#>   X1 X2
#> 1  a  A
#> 2  b  A
#> 3  c  A
#> 4  d  A
#> 5  a  B
#> 6  b  B
#> 7  c  B
#> 8  d  B

# get all pairs of combinations between factors and numerics out of a data.frame
combPairs(which(sapply(CO2, is.numeric)), which(sapply(CO2, is.factor)))
#>   X1 X2
#> 1  4  1
#> 2  5  1
#> 3  4  2
#> 4  5  2
#> 5  4  3
#> 6  5  3