combn {combinat}

Generate all combinations of the elements of x taken m at a time.

Description

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. If argument "fun" is not null, applies a function given by the argument to each point. If simplify is FALSE, returns a list; else returns a vector or an array. "..." are passed unchanged to function given by argument fun, if any.

combn2:Generate all combinations of the elements of x taken two at a time. If x is missing, generate all combinations of 1:n taken two at a time (that is, the indices of x that would give all combinations of the elements of x if x with length n had been given). Exactly one of arguments "x" and "n" should be given; no provisions for function evaluation.

nCm: Compute the binomial coefficient ("n choose m"), where n is any real number and m is any integer. Arguments n and m may be vectors; they will be replicated as necessary to have the same length. Argument tol controls rounding of results to integers. If the difference between a value and its nearest integer is less than tol, the value returned will be rounded to its nearest integer. To turn off rounding, use tol = 0. Values of tol greater than the default should be used only with great caution, unless you are certain only integer values should be returned.

Usage

combn(x, m, fun=NULL, simplify=TRUE, ...)

Arguments

x

vector source for combinations

m

number of elements

fun

function to be applied to each combination (may be null)

simplify

logical, if FALSE, returns a list, otherwise returns vector or array

...

args to fun

Details

Nijenhuis, A. and Wilf, H.S. (1978) Combinatorial Algorithms for Computers and Calculators. NY: Academic Press.

Value

see simplify argument

Author(s)

Code by Scott Chasalow, R package and doc prep by Vince Carey, [e-mail]

References

~put references to the literature/web site here ~

Examples

 combn(letters[1:4], 2)
 combn(10, 5, min)  # minimum value in each combination
# Different way of encoding points:
 combn(c(1,1,1,1,2,2,2,3,3,4), 3, tabulate, nbins = 4)
#Compute support points and (scaled) probabilities for a
#Multivariate-Hypergeometric(n = 3, N = c(4,3,2,1)) p.f.:
# table.mat(t(combn(c(1,1,1,1,2,2,2,3,3,4), 3, tabulate,nbins=4)))