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| using System; | |
| using System.Collections; | |
| using System.Collections.Generic; | |
| using System.Linq; | |
| /* | |
| Some helpful Linq extensions I've used with Unity. | |
| Original code from stackoverflow.com where user contributions are | |
| licensed under CC-BY-SA 3.0 with attribution required. | |
| */ | |
| public static class LinqExtensions { | |
| // http://stackoverflow.com/questions/3645644/whats-your-favorite-linq-to-objects-operator-which-is-not-built-in | |
| /// <summary>Creates a <see cref="Queue<T>"/> from an enumerable | |
| /// collection.</summary> | |
| public static Queue<T> ToQueue<T>(this IEnumerable<T> source) { | |
| if (source == null) | |
| throw new ArgumentNullException("source"); | |
| return new Queue<T>(source); | |
| } | |
| /// <summary>Creates a <see cref="Stack<T>"/> from an enumerable | |
| /// collection.</summary> | |
| public static Stack<T> ToStack<T>(this IEnumerable<T> source) { | |
| if (source == null) | |
| throw new ArgumentNullException("source"); | |
| return new Stack<T>(source); | |
| } | |
| public static bool IsEmpty<T>(this IEnumerable<T> source) { | |
| return !source.Any(); | |
| } | |
| public static void Each<T>(this IEnumerable<T> items, Action<T> action) { | |
| foreach (var i in items) | |
| action(i); | |
| } | |
| /// <summary>Adds a single element to the end of an IEnumerable.</summary> | |
| /// <typeparam name="T">Type of enumerable to return.</typeparam> | |
| /// <returns>IEnumerable containing all the input elements, followed by the | |
| /// specified additional element.</returns> | |
| public static IEnumerable<T> Append<T>(this IEnumerable<T> source, T element) { | |
| if (source == null) | |
| throw new ArgumentNullException("source"); | |
| return concatIterator(element, source, false); | |
| } | |
| /// <summary>Adds a single element to the start of an IEnumerable.</summary> | |
| /// <typeparam name="T">Type of enumerable to return.</typeparam> | |
| /// <returns>IEnumerable containing the specified additional element, followed by | |
| /// all the input elements.</returns> | |
| public static IEnumerable<T> Prepend<T>(this IEnumerable<T> tail, T head) { | |
| if (tail == null) | |
| throw new ArgumentNullException("tail"); | |
| return concatIterator(head, tail, true); | |
| } | |
| private static IEnumerable<T> concatIterator<T>(T extraElement, | |
| IEnumerable<T> source, | |
| bool insertAtStart) { | |
| if (insertAtStart) | |
| yield return extraElement; | |
| foreach (var e in source) | |
| yield return e; | |
| if (!insertAtStart) | |
| yield return extraElement; | |
| } | |
| // http://stackoverflow.com/questions/10206557/c-sharp-cast-dictionarystring-anytype-to-dictionarystring-object-involvin | |
| public static IEnumerable<DictionaryEntry> CastDict(this IEnumerable dictionary) { | |
| foreach (DictionaryEntry entry in dictionary) | |
| { | |
| yield return entry; | |
| } | |
| } | |
| // https://code.msdn.microsoft.com/LINQ-to-DataSets-Custom-41738490 | |
| public static IEnumerable<T2> Combine<T,T2>(this IEnumerable<T> first, | |
| IEnumerable<T> second, | |
| System.Func<T,T,T2> func) { | |
| using (IEnumerator<T> e1 = first.GetEnumerator(), | |
| e2 = second.GetEnumerator()) { | |
| while (e1.MoveNext() && e2.MoveNext()) { | |
| yield return func(e1.Current, e2.Current); | |
| } | |
| } | |
| } | |
| // http://stackoverflow.com/questions/3173718/how-to-get-a-random-object-using-linq | |
| public static T Random<T>(this IEnumerable<T> enumerable) { | |
| var r = new Random(); | |
| var list = enumerable as IList<T> ?? enumerable.ToList(); | |
| return list.ElementAt(r.Next(0, list.Count())); | |
| } | |
| // Reservoir Sampling | |
| // https://en.wikipedia.org/wiki/Reservoir_sampling | |
| /* | |
| Return an IEnumerable with k random items from the given | |
| enumerable with n items. | |
| It's O(n) and doesn't need to get the count n first. | |
| Note: The if the enumerable only has k items, the result will not | |
| be shuffled. | |
| */ | |
| public static IEnumerable<T> Random<T>(this IEnumerable<T> enumerable, | |
| int k) { | |
| var list = new List<T>(k); | |
| using (var e = enumerable.GetEnumerator()) { | |
| for (int i = 0; i < k && e.MoveNext(); i++) | |
| list[i] = e.Current; | |
| var r = new Random(); | |
| int j; | |
| for (int i = k + 1; e.MoveNext(); i++) { | |
| j = r.Next(0, i); // [0, i) | |
| if (j < k) | |
| list[j] = e.Current; | |
| } | |
| return list; | |
| } | |
| } | |
| /* | |
| Behaves like .Skip(count) unless that would skip all the elements, in which | |
| case it returns the last element. | |
| new int[] {0, 1, 2, 3, 4}.Skip(10) -> { } | |
| new int[] {0, 1, 2, 3, 4}.SkipUnlessLast(10) -> { 4 } | |
| But otherwise behaves the same. | |
| new int[] {0, 1, 2, 3, 4}.Skip(2) -> { 2, 3, 4 } | |
| new int[] {0, 1, 2, 3, 4}.SkipUnlessLast(2) -> { 2, 3, 4 } | |
| */ | |
| public static IEnumerable<T> SkipUnlessLast<T>(this IEnumerable<T> source, int count) { | |
| // https://blogs.msmvps.com/jonskeet/2011/01/02/reimplementing-linq-to-objects-part-23-take-skip-takewhile-skipwhile/ | |
| T lastItem = default(T); | |
| using (IEnumerator<T> iterator = source.GetEnumerator()) { | |
| for (int i = 0; i < count; i++) { | |
| if (! iterator.MoveNext()) { | |
| if (i != 0) | |
| yield return lastItem; | |
| yield break; | |
| } else { | |
| lastItem = iterator.Current; | |
| } | |
| } | |
| bool anyMore = false; | |
| while (iterator.MoveNext()) { | |
| anyMore = true; | |
| yield return iterator.Current; | |
| } | |
| if (! anyMore) | |
| yield return lastItem; | |
| } | |
| } | |
| } |
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