This function generates all the combinations of selecting `k`

items from `n`

items.
The results are in lexicographical order.

combinations(x = NULL, k = NULL, n = NULL, v = NULL, freq = NULL, replace = FALSE, layout = NULL, nitem = -1L, skip = NULL, index = NULL, nsample = NULL, drop = NULL)

x | an integer or a vector, will be treated as |
---|---|

k | an integer, the number of items drawn, defaults to |

n | an integer, the total number of items, its value may be implicitly deduced from |

v | a vector to be drawn, defaults to |

freq | an integer vector of item repeat frequencies |

replace | an logical to draw items with replacement |

layout | if "row", "column" or "list" is specified, the returned value would be a "row-major" matrix, a "column-major" matrix or a list respectively |

nitem | number of combinations required, usually used with |

skip | the number of combinations skipped |

index | a vector of indices of the desired combinations |

nsample | sampling random combinations |

drop | vectorize a matrix or unlist a list |

icombinations for iterating combinations and ncombinations to calculate number of combinations

# choose 2 from 4 combinations(4, 2)#> [,1] [,2] #> [1,] 1 2 #> [2,] 1 3 #> [3,] 1 4 #> [4,] 2 3 #> [5,] 2 4 #> [6,] 3 4combinations(LETTERS[1:3], k = 2)#> [,1] [,2] #> [1,] "A" "B" #> [2,] "A" "C" #> [3,] "B" "C"#> [,1] [,2] [,3] #> [1,] 1 1 2 #> [2,] 1 2 2 #> [3,] 2 2 2# with replacement combinations(4, 2, replace = TRUE)#> [,1] [,2] #> [1,] 1 1 #> [2,] 1 2 #> [3,] 1 3 #> [4,] 1 4 #> [5,] 2 2 #> [6,] 2 3 #> [7,] 2 4 #> [8,] 3 3 #> [9,] 3 4 #> [10,] 4 4# column major combinations(4, 2, layout = "column")#> [,1] [,2] [,3] [,4] [,5] [,6] #> [1,] 1 1 1 2 2 3 #> [2,] 2 3 4 3 4 4# list output combinations(4, 2, layout = "list")#> [[1]] #> [1] 1 2 #> #> [[2]] #> [1] 1 3 #> #> [[3]] #> [1] 1 4 #> #> [[4]] #> [1] 2 3 #> #> [[5]] #> [1] 2 4 #> #> [[6]] #> [1] 3 4 #># specifc range of combinations combinations(4, 2, nitem = 2, skip = 3)#> [,1] [,2] #> [1,] 2 3 #> [2,] 2 4#> [,1] [,2] #> [1,] 1 4 #> [2,] 2 4# random combinations combinations(4, 2, nsample = 3)#> [,1] [,2] #> [1,] 1 2 #> [2,] 3 4 #> [3,] 2 3#> [1] 1 0#> [1] 0 6#> [1] 1 0#> [1] 0 1