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#region License and Terms
// 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.
#endregion
namespace MoreLinq
{
using System;
using System.Collections.Generic;
static partial class MoreEnumerable
{
/// <summary>
/// Returns the minimal elements of the given sequence, based on
/// the given projection.
/// </summary>
/// <remarks>
/// This overload uses the default comparer for the projected type.
/// This operator uses deferred execution. The results are evaluated
/// and cached on first use to returned sequence.
/// </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="selector">Selector to use to pick the results to compare</param>
/// <returns>The sequence of minimal elements, according to the projection.</returns>
/// <exception cref="ArgumentNullException"><paramref name="source"/> or <paramref name="selector"/> is null</exception>
public static IExtremaEnumerable<TSource> MinBy<TSource, TKey>(this IEnumerable<TSource> source,
Func<TSource, TKey> selector)
{
return source.MinBy(selector, null);
}
/// <summary>
/// Returns the minimal elements of the given sequence, based on
/// the given projection and the specified comparer for projected values.
/// </summary>
/// <remarks>
/// This operator uses deferred execution. The results are evaluated
/// and cached on first use to returned sequence.
/// </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="selector">Selector to use to pick the results to compare</param>
/// <param name="comparer">Comparer to use to compare projected values</param>
/// <returns>The sequence of minimal elements, according to the projection.</returns>
/// <exception cref="ArgumentNullException"><paramref name="source"/>, <paramref name="selector"/>
/// or <paramref name="comparer"/> is null</exception>
public static IExtremaEnumerable<TSource> MinBy<TSource, TKey>(this IEnumerable<TSource> source,
Func<TSource, TKey> selector, IComparer<TKey>? comparer)
{
if (source == null) throw new ArgumentNullException(nameof(source));
if (selector == null) throw new ArgumentNullException(nameof(selector));
comparer ??= Comparer<TKey>.Default;
return new ExtremaEnumerable<TSource, TKey>(source, selector, (x, y) => -Math.Sign(comparer.Compare(x, y)));
}
}
}