Linq中Take、TakeWhile、Skip、SkipWhile的比较

以下代码均来自微软官网

/// <summary>

/// This sample uses
Take 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 uses
TakeWhile 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 uses
Skip 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);

}