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 |

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

P. T. Wallace and Søren Højsgaard

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | ```
x <- letters[1:20]
m <- 3
combn(x,m)
combnPrim(x,m)
combn(m,m)
combnPrim(m,m)
combn(x,m, simplify=FALSE)
combnPrim(x,m, simplify=FALSE)
system.time({ for (i in 1:100) { combnPrim(x,m) }})
system.time({ for (i in 1:100) { combn(x,m) }})
system.time({ for (i in 1:100) { combnPrim(x,m, simplify=FALSE) }})
system.time({ for (i in 1:100) { combn(x,m, simplify=FALSE) }})
``` |

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