2

2 つのリストを比較したい。List2 に List1 の項目があるかどうかを確認したいと思います。予想外の結果が得られました。以下の私のコードを見てください。

テスト コード クラス

class Program
{
    static void Main(string[] args)
    {
        bool loop = true;
        int textcount = 1;
        while (loop)
        {

            var collection1 = GetCollection();
            var collection2 = GetCollection();

            Console.WriteLine("Test No " + textcount.ToString());


            Console.WriteLine("Collection 1 =" + String.Join(", ", collection1.ToArray()));

            Console.WriteLine("Collection 2 =" + String.Join(", ", collection2.ToArray()));

            System.Diagnostics.Stopwatch watch = new System.Diagnostics.Stopwatch();
            watch.Start();
            var hasitem = collection1.Any(item => collection2.Contains(item));

            watch.Stop();

            Console.WriteLine(hasitem.ToString() + "  Found in " + watch.ElapsedTicks.ToString());
            watch.Reset();

            watch.Start();
            var hasAtLeastOne = collection1.Intersect(collection2).Any();
            watch.Stop();
            Console.WriteLine(hasAtLeastOne.ToString() + "  With Intersect Found in " + watch.ElapsedTicks.ToString());
            textcount++;
            Console.ReadKey();
        }


    }
    static Random ran = new Random();
    private static IEnumerable<int> GetCollection()
    {
        for (int i = 0; i < 5; i++)
        {
            yield return ran.Next(i, 20);
        }
    }
}

そして結果は非常に迷惑です。最後の 4 つの結果を参照してください。

Test No 1
Collection 1 =10, 8, 18, 6, 11
Collection 2 =3, 12, 18, 13, 6
True  Found in 3075
True  With Intersect Found in 15297
 Test No 2
Collection 1 =18, 13, 7, 18, 5
Collection 2 =12, 18, 8, 3, 5
True  Found in 22
True  With Intersect Found in 100
 Test No 3
Collection 1 =1, 6, 15, 7, 9
Collection 2 =16, 15, 14, 14, 12
True  Found in 21
True  With Intersect Found in 23
 Test No 4
Collection 1 =3, 16, 7, 4, 19
Collection 2 =6, 3, 15, 15, 9
True  Found in 21
True  With Intersect Found in 56
 Test No 5
Collection 1 =18, 18, 9, 17, 10
Collection 2 =17, 12, 4, 3, 11
True  Found in 25
True  With Intersect Found in 20
 Test No 6
Collection 1 =9, 9, 2, 17, 19
Collection 2 =17, 2, 18, 3, 15
False  Found in 109
False  With Intersect Found in 41
 Test No 7
Collection 1 =3, 15, 3, 5, 5
Collection 2 =2, 2, 11, 7, 6
True  Found in 22
False  With Intersect Found in 15
 Test No 8
Collection 1 =7, 14, 17, 14, 18
Collection 2 =18, 4, 7, 18, 16
False  Found in 28
True  With Intersect Found in 19
 Test No 9
Collection 1 =3, 9, 6, 18, 9
Collection 2 =10, 3, 17, 17, 18
True  Found in 28
True  With Intersect Found in 22
 Test No 10
Collection 1 =15, 18, 2, 9, 8
Collection 2 =10, 15, 3, 10, 19
False  Found in 135
True  With Intersect Found in 128
 Test No 11
Collection 1 =6, 2, 17, 18, 18
Collection 2 =14, 16, 14, 6, 4
False  Found in 20
False  With Intersect Found in 17
4

2 に答える 2

0

これはあなたの問題です：

private static IEnumerable<int> GetCollection()
{
    for (int i = 0; i < 5; i++)
    {
        yield return ran.Next(i, 20);
    }
}

これにします：

private static List<int> GetCollection()
{
  return new List<int>
         {
           ran.Next(0, 20),
           ran.Next(1, 20),
           ran.Next(2, 20),
           ran.Next(3, 20),
           ran.Next(4, 20)
         };
}

そして、あなたの問題は消えます。

長い説明は、IEnumerable 関数を作成すると、さまざまな LINQ 呼び出しで反復子を繰り返し呼び出すことが期待できるということです (結局のところ、それが IEnumerable の機能ですよね?)。yield return <some random number>各イテレータ呼び出しで実行するため、不安定な結果が予想されます。結果への参照を保存するか.ToArray()、安定したリストを返すのが最善です。

于 2013-04-09T13:08:15.110 に答える