Linq中Take、TakeWhile、Skip、SkipWhile的比较

以下代码均来自微软官网
/// <summary>
/// This sample usesTake to get only the first 3 elements of the array.
/// </summary>
public void Linq1()
{
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
    var first3Numbers = numbers.Take(3); //从第一个元素开始,获取三个

    Console.WriteLine("First 3 numbers:");

    foreach (var n in first3Numbers)
    {
        Console.WriteLine(n);
    }
}

result-----
First 3 numbers:
5
4
1

/// <summary>
/// This sample usesTakeWhile to return elements starting from the beginning
/// of the array until a number is hit that is not less than 6
/// </summary>
public void Linq2()
{
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };

    //在这里需要注意.使用TakeWhile获取小于6的元素,是从第一个元素开始,
    //一直到不满足其小于6这个条件为止.也就是执行到和9这个元素比较后,就结束比较了
    //可以想象一下执行过程.
    //5<6=true;4<6=true;1<6=true;3<6=true
    //9<6=false;   这里就停止继续比较了
    var firstNumbersLessThan6 = numbers.TakeWhile(n => n < 6);

    Console.WriteLine("First numbers less than 6:");

    foreach (var n in firstNumbersLessThan6)
    {
        Console.WriteLine(n);
    }
}

result----
First numbers less than 6:
5
4
1
3

/// <summary>
/// This sample usesSkip to get all but the first 4 elements of the array
/// </summary>
public void Linq3()
{
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
    var allButFirst4Numbers = numbers.Skip(4);  //跳过前四个元素,获取后面所有的元素

    Console.WriteLine("All but first 4 numbers:");

    foreach (var n in allButFirst4Numbers)
    {
        Console.WriteLine(n);
    }
}

result---
All but first 4 numbers:
9
8
6
7
2
0

/// <summary>
/// This sample uses SkipWhile to get the elements of the array starting from the first element divisible by 3.
/// </summary>
public void Linq4()
{
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };

    //跳过不能被3整除的所有元素
    //这里和TakeWhiel又有些不一样。
    //TakeWhile遇到条件不满足的时候,就会return,
    //但是SkipWhile如果执行到能被三整除的数,那么其后面的元素就不会继续比较了
    //同样,想象一下执行过程
    //5%3!=0==true;     4%3!=0==true;   1%3!=0==true;
    //3%3!=0==false;  运行到这里的时候,后面的就不再比较.
    //所以输出结果中会有8、7、2、0这几个不满足条件的元素
    var allButFirst3Numbers = numbers.SkipWhile(n => n % 3 != 0);

Console.WriteLine("All elements starting from first element divisible by 3:");
    foreach (var n in allButFirst3Numbers)
    {
        Console.WriteLine(n);
    }

}

result---
All elements starting from first element divisible by 3:
3
9
8
6
7
2
0

 

   public ElectrostaticCapacityTestResultData LeastSquaresMethod(float voltage, int point, bool isBalanced)
        {
            var tempData = new List<Tuple<double, double>>();

            var normalData = this.Result.Where((item) => isBalanced ? item.CapacitanceDataState == "N" && item.TanDeltaDataState == "N" : true);

            // 
            var item1 = normalData.TakeWhile((item) => item.Voltage <= voltage).ToList();
            var item2 = normalData.SkipWhile((item) => item.Voltage <= voltage).ToList();

            // 
            if (item1.Count < point || item2.Count < point)
            {
                return null;
            }

            // 
            item1
                .Skip(item1.Count - point)
                .ForEach((item) => tempData.Add(new Tuple<double, double>(item.Voltage, item.TanDelta)));

            item2
                .Take(point)
                .ForEach((item) => tempData.Add(new Tuple<double, double>(item.Voltage, item.TanDelta)));

            double slope;
            double intercept;

            Common.Math.CalcSlopeAndIntercept(tempData, out slope, out intercept);

            // 
            if (double.IsNaN(slope) || double.IsNaN(intercept))
            {
                return null;
            }

            float tanDelta = ((slope * voltage) + intercept).ToFloat();

            tempData.Clear();

            // 
            item1
                .Skip(item1.Count - point)
                .ForEach((item) => tempData.Add(new Tuple<double, double>(item.Voltage, item.Capacity)));

            item2
                .Take(point)
                .ForEach((item) => tempData.Add(new Tuple<double, double>(item.Voltage, item.Capacity)));

            Common.Math.CalcSlopeAndIntercept(tempData, out slope, out intercept);

            // 
            if (double.IsNaN(slope) || double.IsNaN(intercept))
            {
                return null;
            }

            float capacity = ((slope * voltage) + intercept).ToFloat();

            return new ElectrostaticCapacityTestResultData(voltage, capacity, tanDelta);
        }