Data.Choose

Immutable combinations.

Combinations

data Choose

The immutable combination data type. A way of representing k unordered outcomes from n possiblities. The possibilites are represented as the indices 0, ..., n-1, and the outcomes are given as a subset of size k. The subset is stored with the indices in ascending order.

Instances

Eq Choose

Show Choose

Creating combinations

choose :: Int -> Int -> Choose

choose n k returns the first combination of k outcomes from n possibilites, namely the subset { 0, ..., k-1 }.

listChoose :: Int -> Int -> [Int] -> Choose

Construct a combination from a list of elements. listChoose n k is creates a combination of k outcomes from n possibilities initialized to have the ith element equal to is !! i. For the combination to be valid, the elements must all be unique, they must be in sorted order, and they all must be in the range 0 .. n-1.

Accessing combination elements

at :: Choose -> Int -> Int

at c i gets the value of the ith element of the combination c. The index i must be in the range 0..(k-1), where k is the size of the combination.

unsafeAt :: Choose -> Int -> Int

Combination properties

possible :: Choose -> Int

Get the number of possibilities, n.

size :: Choose -> Int

Get the number of outcomes, k.

elems :: Choose -> [Int]

Get a list of the k outcomes.

Combination functions

complement :: Choose -> Choose

Get the inverse of a combination

complElems :: Choose -> [Int]

Get a list of the elements in the complement of a combination. If the combination is a subset of k outcomes from n possibilities, then the returned list will be sorted and of length n-k.

next :: Choose -> Maybe Choose

Return the next combination in lexicographic order, or Nothing if there are no further combinations. Starting with the first combination and repeatedly calling this function will iterate through all combinations of a given order.

prev :: Choose -> Maybe Choose

Return the previous combination in lexicographic order, or Nothing if such combination exists.