R: Enumerate the Combinations or Permutations of the Elements of...
combinations
R Documentation
Enumerate the Combinations or Permutations of the Elements of a Vector
Description
combinations enumerates the possible combinations of a
specified size from the elements of a vector. permutations
enumerates the possible permutations.
Logical flag indicating whether duplicates should be
removed from the source vector v. Defaults to TRUE.
repeats.allowed
Logical flag indicating whether the
constructed vectors may include duplicated values. Defaults to
FALSE.
Details
Caution: The number of combinations and permutations increases rapidly
with n and r!.
To use values of n above about 45, you will need to increase
R's recursion limit. See the expression argument to the
options command for details on how to do this.
Value
Returns a matrix where each row contains a vector of length r.
combinations(3,2,letters[1:3])
combinations(3,2,letters[1:3],repeats=TRUE)
permutations(3,2,letters[1:3])
permutations(3,2,letters[1:3],repeats=TRUE)
# To use large 'n', you need to change the default recusion limit
options(expressions=1e5)
cmat <- combinations(300,2)
dim(cmat) # 44850 by 2