arrangements: combinations – R documentation

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combinations

Combinations generator

Description

This function generates all the combinations of selecting k items from n items. The results are in lexicographical order.

Usage

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)

Arguments

`x`	an integer or a vector, will be treated as `n` if integer; otherwise, will be treated as `v`. Should not be specified together with `n` and `v`.
`k`	an integer, the number of items drawn, defaults to `n` if `freq` is `NULL` else `sum(freq)`
`n`	an integer, the total number of items, its value may be implicitly deduced from `length(v)` or `length(freq)`
`v`	a vector to be drawn, defaults to `1:n`.
`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`
`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

Examples

# choose 2 from 4
combinations(4, 2)
combinations(LETTERS[1:3], k = 2)

# multiset with frequencies c(2, 3)
combinations(k = 3, freq = c(2, 3))

# with replacement
combinations(4, 2, replace = TRUE)

# column major
combinations(4, 2, layout = "column")

# list output
combinations(4, 2, layout = "list")

# specifc range of combinations
combinations(4, 2, nitem = 2, skip = 3)

# specific combinations
combinations(4, 2, index = c(3, 5))

# random combinations
combinations(4, 2, nsample = 3)

# zero sized combinations
dim(combinations(5, 0))
dim(combinations(5, 6))
dim(combinations(0, 0))
dim(combinations(0, 1))

arrangements

Fast Generators and Iterators for Permutations, Combinations, Integer Partitions and Compositions

v1.1.9

MIT + file LICENSE

Authors

Randy Lai [aut, cre]

Initial release

2020-09-12