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