arrangements (version 1.1.7)

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 = n, 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

k

an integer, the number of items drawn

n

an integer, the total number of items, its actual value may be determined by other variables

v

a vector to be drawn

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

See Also

icombinations for iterating combinations and ncombinations to calculate number of combinations

Examples

# NOT RUN {
# 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))

# }