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86 lines
4.0 KiB
86 lines
4.0 KiB
using System;
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using System.Collections.Generic;
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// TODO: @bond Remove
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namespace MediaBrowser.Model.Extensions
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{
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// MoreLINQ - Extensions to LINQ to Objects
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// Copyright (c) 2008 Jonathan Skeet. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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public static class LinqExtensions
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{
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/// <summary>
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/// Returns all distinct elements of the given source, where "distinctness"
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/// is determined via a projection and the default equality comparer for the projected type.
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/// </summary>
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/// <remarks>
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/// This operator uses deferred execution and streams the results, although
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/// a set of already-seen keys is retained. If a key is seen multiple times,
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/// only the first element with that key is returned.
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/// </remarks>
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/// <typeparam name="TSource">Type of the source sequence</typeparam>
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/// <typeparam name="TKey">Type of the projected element</typeparam>
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/// <param name="source">Source sequence</param>
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/// <param name="keySelector">Projection for determining "distinctness"</param>
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/// <returns>A sequence consisting of distinct elements from the source sequence,
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/// comparing them by the specified key projection.</returns>
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public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source,
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Func<TSource, TKey> keySelector)
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{
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return source.DistinctBy(keySelector, null);
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}
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/// <summary>
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/// Returns all distinct elements of the given source, where "distinctness"
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/// is determined via a projection and the specified comparer for the projected type.
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/// </summary>
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/// <remarks>
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/// This operator uses deferred execution and streams the results, although
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/// a set of already-seen keys is retained. If a key is seen multiple times,
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/// only the first element with that key is returned.
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/// </remarks>
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/// <typeparam name="TSource">Type of the source sequence</typeparam>
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/// <typeparam name="TKey">Type of the projected element</typeparam>
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/// <param name="source">Source sequence</param>
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/// <param name="keySelector">Projection for determining "distinctness"</param>
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/// <param name="comparer">The equality comparer to use to determine whether or not keys are equal.
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/// If null, the default equality comparer for <c>TSource</c> is used.</param>
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/// <returns>A sequence consisting of distinct elements from the source sequence,
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/// comparing them by the specified key projection.</returns>
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public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source,
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Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)
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{
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if (source == null) throw new ArgumentNullException(nameof(source));
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if (keySelector == null) throw new ArgumentNullException(nameof(keySelector));
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return DistinctByImpl(source, keySelector, comparer);
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}
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private static IEnumerable<TSource> DistinctByImpl<TSource, TKey>(IEnumerable<TSource> source,
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Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)
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{
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var knownKeys = new HashSet<TKey>(comparer);
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foreach (var element in source)
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{
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if (knownKeys.Add(keySelector(element)))
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{
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yield return element;
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}
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}
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}
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}
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}
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