85 lines
4.0 KiB
C#
85 lines
4.0 KiB
C#
|
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;
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
}
|