【C#】シーケンスの要素が重複している場合 true を返す拡張メソッド

ソースコード

using System;
using System.Collections.Generic;
using System.Linq;

public static class IEnumerableExt
{
    public static bool HasDuplication<TKey, TSource>
    (
        this IEnumerable<TSource> self,
        Func<TSource, TKey>       keySelector
    )
    {
        return self
                .GroupBy( keySelector )
                .Any( x => 1 < x.Count() )
            ;
    }

    public static bool HasDuplication<TSource>
    (
        this IEnumerable<TSource> self
    )
    {
        return self
                .GroupBy( x => x )
                .Any( x => 1 < x.Count() )
            ;
    }

使用例

var list1 = new[] { 1, 2, 3 };

Debug.Log( list1.HasDuplication() );

var list2 = new[] { 1, 1, 1 };

Debug.Log( list2.HasDuplication() );

var list3 = new[]
{
    ( Id: 1, Name: "フシギダネ" ),
    ( Id: 2, Name: "フシギソウ" ),
    ( Id: 3, Name: "フシギバナ" ),
};

Debug.Log( list3.HasDuplication( x => x.Id ) );

var list4 = new[]
{
    ( Id: 1, Name: "フシギダネ" ),
    ( Id: 1, Name: "フシギダネ" ),
    ( Id: 1, Name: "フシギダネ" ),
};

Debug.Log( list4.HasDuplication( x => x.Id ) );

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