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MinBy.cs
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MinBy.cs
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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 element of the given sequence, based on
/// the given projection.
/// </summary>
/// <remarks>
/// If more than one element has the minimal projected value, the first
/// one encountered will be returned. This overload uses the default comparer
/// for the projected type. This operator uses immediate execution, but
/// only buffers a single result (the current minimal element).
/// </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 minimal element, according to the projection.</returns>
/// <exception cref="ArgumentNullException"><paramref name="source"/> or <paramref name="selector"/> is null</exception>
/// <exception cref="InvalidOperationException"><paramref name="source"/> is empty</exception>
public static TSource MinBy<TSource, TKey>(this IEnumerable<TSource> source,
Func<TSource, TKey> selector)
{
return source.MinBy(selector, null);
}
/// <summary>
/// Returns the minimal element of the given sequence, based on
/// the given projection and the specified comparer for projected values.
/// </summary>
/// <remarks>
/// If more than one element has the minimal projected value, the first
/// one encountered will be returned. This operator uses immediate execution, but
/// only buffers a single result (the current minimal element).
/// </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 minimal element, according to the projection.</returns>
/// <exception cref="ArgumentNullException"><paramref name="source"/>, <paramref name="selector"/>
/// or <paramref name="comparer"/> is null</exception>
/// <exception cref="InvalidOperationException"><paramref name="source"/> is empty</exception>
public static TSource MinBy<TSource, TKey>(this IEnumerable<TSource> source,
Func<TSource, TKey> selector, IComparer<TKey> comparer)
{
if (source == null) throw new ArgumentNullException("source");
if (selector == null) throw new ArgumentNullException("selector");
comparer = comparer ?? Comparer<TKey>.Default;
using (var sourceIterator = source.GetEnumerator())
{
if (!sourceIterator.MoveNext())
{
throw new InvalidOperationException("Sequence contains no elements");
}
var min = sourceIterator.Current;
var minKey = selector(min);
while (sourceIterator.MoveNext())
{
var candidate = sourceIterator.Current;
var candidateProjected = selector(candidate);
if (comparer.Compare(candidateProjected, minKey) < 0)
{
min = candidate;
minKey = candidateProjected;
}
}
return min;
}
}
}
}