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80 lines
4 KiB
C#
80 lines
4 KiB
C#
using System.Collections.Generic;
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using System.Linq;
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namespace MLEM.Extensions {
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/// <summary>
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/// A set of extensions for dealing with collections of various kinds
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/// </summary>
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public static class CollectionExtensions {
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/// <summary>
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/// This method returns a set of possible combinations of n items from n different sets, where the order of the items in each combination is based on the order of the input sets.
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/// For a version of this method that returns indices rather than entries, see <see cref="IndexCombinations{T}"/>.
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/// <example>
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/// Given the input set <c>{{1, 2, 3}, {A, B}, {+, -}}</c>, the returned set would contain the following sets:
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/// <code>
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/// {1, A, +}, {1, A, -}, {1, B, +}, {1, B, -},
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/// {2, A, +}, {2, A, -}, {2, B, +}, {2, B, -},
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/// {3, A, +}, {3, A, -}, {3, B, +}, {3, B, -}
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/// </code>
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/// </example>
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/// </summary>
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/// <param name="things">The different sets to be combined</param>
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/// <typeparam name="T">The type of the items in the sets</typeparam>
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/// <returns>All combinations of set items as described</returns>
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public static IEnumerable<IEnumerable<T>> Combinations<T>(this IEnumerable<IEnumerable<T>> things) {
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var combos = Enumerable.Repeat(Enumerable.Empty<T>(), 1);
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foreach (var t in things)
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combos = combos.SelectMany(c => t.Select(c.Append));
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return combos;
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}
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/// <summary>
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/// This method returns a set of possible combinations of n indices of items from n different sets, where the order of the items' indices in each combination is based on the order of the input sets.
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/// For a version of this method that returns entries rather than indices, see <see cref="Combinations{T}"/>.
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/// <example>
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/// Given the input set <c>{{1, 2, 3}, {A, B}, {+, -}}</c>, the returned set would contain the following sets:
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/// <code>
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/// {0, 0, 0}, {0, 0, 1}, {0, 1, 0}, {0, 1, 1},
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/// {1, 0, 0}, {1, 0, 1}, {1, 1, 0}, {1, 1, 1},
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/// {2, 0, 0}, {2, 0, 1}, {2, 1, 0}, {2, 1, 1}
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/// </code>
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/// </example>
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/// </summary>
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/// <param name="things">The different sets to be combined</param>
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/// <typeparam name="T">The type of the items in the sets</typeparam>
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/// <returns>All combinations of set items as described</returns>
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public static IEnumerable<IEnumerable<int>> IndexCombinations<T>(this IEnumerable<IEnumerable<T>> things) {
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var combos = Enumerable.Repeat(Enumerable.Empty<int>(), 1);
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foreach (var t in things)
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combos = combos.SelectMany(c => t.Select((o, i) => c.Append(i)));
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return combos;
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}
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#if NET452
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/// <summary>Appends a value to the end of the sequence.</summary>
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/// <param name="source">A sequence of values.</param>
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/// <param name="element">The value to append to <paramref name="source"/>.</param>
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/// <typeparam name="T">The type of the elements of <paramref name="source"/>.</typeparam>
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/// <returns>A new sequence that ends with <paramref name="element"/>.</returns>
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public static IEnumerable<T> Append<T>(this IEnumerable<T> source, T element) {
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foreach (var src in source)
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yield return src;
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yield return element;
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}
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/// <summary>Prepends a value to the beginning of the sequence.</summary>
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/// <param name="source">A sequence of values.</param>
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/// <param name="element">The value to prepend to <paramref name="source"/>.</param>
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/// <typeparam name="T">The type of the elements of <paramref name="source"/>.</typeparam>
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/// <returns>A new sequence that begins with <paramref name="element"/>.</returns>
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public static IEnumerable<T> Prepend<T>(this IEnumerable<T> source, T element) {
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yield return element;
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foreach (var src in source)
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yield return src;
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}
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#endif
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}
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}
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