Linq中的Where與SkipWhile

      本文將介紹Linq中的Where與SkipWhile的用法，有時我們容易混淆它們。下面來看一個簡單的UnitTest:

[TestMethod]
public void TestSkipWhileAndWhereLinq()
{
    //arrange
    string[] names = { "Jalpesh", "Jayesh", "Tushar", "Tejas", "Sanjay", "Nijesh", "Jemit", "Jay" }; 

    var skipWhileResult = names.SkipWhile(s => s.ToLower().StartsWith("j"));
    //assert
    var expectArray=new string[] {"Tushar", "Tejas", "Sanjay", "Nijesh", "Jemit", "Jay" };
    CollectionAssert.AreEqual( expectArray, skipWhileResult.ToArray());

    var whereReuslt = names.Where(s => !s.ToLower().StartsWith("j"));
    //assert
    var expectArray2 = new string[] { "Tushar", "Tejas", "Sanjay", "Nijesh" };
    CollectionAssert.AreEqual(expectArray2, whereReuslt.ToArray());
}

  SkipWhile只是匹配一開始滿足條件的元素。上面的代碼一看就明白。更加請參照MSDN

  SkipWhile是這樣的實現的:

 

public static IEnumerable<TSource> SkipWhile<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
{
    if (source == null) throw Error.ArgumentNull("source");
    if (predicate == null) throw Error.ArgumentNull("predicate");
    return SkipWhileIterator<TSource>(source, predicate);
}

private static IEnumerable<TSource> SkipWhileIterator<TSource>(IEnumerable<TSource> source, Func<TSource, bool> predicate)
{
    bool iteratorVariable0 = false;
    foreach (TSource iteratorVariable1 in source)
    {
        if (!iteratorVariable0 && !predicate(iteratorVariable1)) iteratorVariable0 = true;
        if (iteratorVariable0)
        {
            yield return iteratorVariable1;
        }
    }
}

 

  希望對您開發有幫助。 

作者：Petter Liu
出處：http://www.cnblogs.com/wintersun/
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