I'm trying to write an algorithm to select all combinations of n values from a set of numbers.
For instance, given the set: 1, 2, 3, 7, 8, 9
All combinations of 2 values from the set is:
(1, 2), (1, 3), (1, 7), (1, 8), (1, 9), (2, 3), (2, 7), (2, 8), (2, 9), (3, 7), (3, 8), (3, 9), (7, 8), (7, 9), (8, 9)
And 3 is:
(1, 2, 3), (1, 2, 7), (1, 2, 8), (1, 2, 9), (1, 3, 7), (1, 3, 8), (1, 3, 9), (1, 7, 8), (1, 7, 9), (1, 8, 9), (2, 3, 7), (2, 3, 8), (2, 3, 9), (2, 7, 8), (2, 7, 9), (2, 8, 9), (3, 7, 8), (3, 7, 9), (3, 8, 9), (7, 8, 9)
etc!
I'm currently using methods to to yield return sets of combinations of 2, 3 and 4 values, but it seems to me this could be generalised in a LINQ query.
Thanks for your help!
All Method: The All method of System. LINQ. Queryable class returns a Boolean value if all the elements of the sequence satisfy the provided condition. It returns true if all the elements satisfy the condition otherwise it returns false.
The Any operator is used to check whether any element in the sequence or collection satisfy the given condition. If one or more element satisfies the given condition, then it will return true. If any element does not satisfy the given condition, then it will return false.
Usage:
var results = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 }.DifferentCombinations(3);
Code:
public static class Ex
{
public static IEnumerable<IEnumerable<T>> DifferentCombinations<T>(this IEnumerable<T> elements, int k)
{
return k == 0 ? new[] { new T[0] } :
elements.SelectMany((e, i) =>
elements.Skip(i + 1).DifferentCombinations(k - 1).Select(c => (new[] {e}).Concat(c)));
}
}
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