combn_prim: Generate All Combinations of n Elements Taken m at a Time
In DataSciBurgoon/gRbase: A Package for Graphical Modelling in R

Description Usage Arguments Value Note Author(s) See Also Examples

Generate all combinations of the elements of x taken m at a time. If x is a positive integer, returns all combinations of the elements of seq(x) taken m at a time.

1	combn_prim(x, m, simplify = TRUE)

`x`	vector source for combinations, or integer n for x <- seq(n).
`m`	number of elements to choose.
`simplify`	logical indicating if the result should be simplified to a matrix; if FALSE, the function returns a list.

A matrix or a list.

The combn_prim function is a simplified version of the combn function. However, combn_prim is implemented in C and is considerably faster than combn.

P. T. Wallace and Søren Højsgaard

combn

x <- letters[1:5]
m <- 3

combn(x, m)
combn_prim(x, m)

combn(m, m)
combn_prim(m, m)

combn(x, m, simplify=FALSE)
combn_prim(x, m, simplify=FALSE)

x <- letters[1:20]

## Not run: 
system.time({ for (i in 1:100) { combn_prim(x,m) }})
system.time({ for (i in 1:100) { combn(x,m) }})

system.time({ for (i in 1:100) { combn_prim(x,m, simplify=FALSE) }})
system.time({ for (i in 1:100) { combn(x,m, simplify=FALSE) }})

## End(Not run)