Number of combinations

Number of combinations

ncombinations(x = NULL, k = NULL, n = NULL, v = NULL,
  freq = NULL, replace = FALSE, bigz = FALSE)

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
bigz	an logical to use gmp::bigz

See also

combinations for generating all combinations and icombinations for iterating combinations

Examples

ncombinations(5, 2)
#> [1] 10
ncombinations(LETTERS, k = 5)
#> [1] 65780

# integer overflow
if (FALSE) ncombinations(40, 15)
ncombinations(40, 15, bigz = TRUE)
#> Big Integer ('bigz') :
#> [1] 40225345056

# number of combinations of `c("a", "b", "b")`
# they are `c("a", "b")` and `c("b", "b")`
ncombinations(k = 2, freq = c(1, 2))
#> [1] 2

# zero sized combinations
ncombinations(5, 0)
#> [1] 1
ncombinations(5, 6)
#> [1] 0
ncombinations(0, 1)
#> [1] 0
ncombinations(0, 0)
#> [1] 1