List<string>常用操作

1.定义变量

IEnumerable<string> lstNew = null;

List<string> lstOne = new List<string>(){"January", "February", "March"};

List<string> lstTwo = new List<string>() { "January", "April", "March"};

List<string> lstThree = new List<string>() { "January", "April", "March", "May" };

List<string> lstFour = new List<string>() { "Jan", "Feb", "Jan", "April", "Feb" };

2.输入

static void PrintList(IEnumerable<string> str)

{

foreach (var s in str)

Console.WriteLine(s);

Console.WriteLine("-------------");

}

3.常用操作(命名空间:System.Linq)

      Enumberable.Intersect();

     // Compare two List<string> and display common elements

lstNew = lstOne.Intersect(lstTwo, StringComparer.OrdinalIgnoreCase);

PrintList(lstNew);

输出相同元素:JANUARY MARCH

• Enumerable.Except

// Compare two List<string> and display items of lstOne not in lstTwo

lstNew = lstOne.Except(lstTwo, StringComparer.OrdinalIgnoreCase);

PrintList(lstNew);

• Enumerable.Distinct

// Unique List<string>

lstNew = lstFour.Distinct(StringComparer.OrdinalIgnoreCase);

PrintList(lstNew)

• List.ConvertAll

// Convert elements of List<string> to Upper Case

lstNew = lstOne.ConvertAll(x => x.ToUpper());

PrintList(lstNew);

• Enumerable.Concat

// Concatenate and Sort two List<string>

lstNew = lstOne.Concat(lstTwo).OrderBy(s => s);

PrintList(lstNew);

• Enumerable.Concat and Enumerable.Distinct

// Concatenate Unique Elements of two List<string>

lstNew = lstOne.Concat(lstTwo).Distinct();

PrintList(lstNew);

• List.Reverse

// Reverse a List<string>

lstOne.Reverse();

PrintList(lstOne);

• List.RemoveAll

// Search a List<string> and Remove the Search Item

// from the List<string>

int cnt = lstFour.RemoveAll(x => x.Contains("Feb"));

Console.WriteLine("{0} items removed", cnt);

PrintList(lstFour);

•  Enumerable.OrderBy and Enumerable.ThenByDescending

// Order by Length then by words (descending)

lstNew = lstThree.OrderBy(x => x.Length)

        .ThenByDescending(x => x);

PrintList(lstNew);

• Use the Enumerable.Aggregate method

C#

// Create a string by combining all words of a List<string>

// Use StringBuilder if you want performance

string delim = ",";

var str = lstOne.Aggregate((x, y) => x + delim + y);

Console.WriteLine(str);

Console.WriteLine("-------------");

• Split the string and use the Enumerable.ToList method

C#

// Create a List<string> from a Delimited string

string s = "January February March";

char separator = ' ';

lstNew = s.Split(separator).ToList();

PrintList(lstNew);

Use the List(T).ConvertAll method

C#

// Convert a List<int> to List<string>

List<int> lstNum = new List<int>(new int[] { 3, 6, 7, 9 });

lstNew = lstNum.ConvertAll<string>(delegate(int i)

{

return i.ToString();

});

PrintList(lstNew);

• Use Enumerable.GroupBy, Enumerable.Select and Enumerable.OrderByDescending

// Count Repeated Words

var q = lstFour.GroupBy(x => x)

   .Select(g => new { Value = g.Key, Count = g.Count() })

   .OrderByDescending(x => x.Count);

foreach (var x in q)

{

     Console.WriteLine("Value: " + x.Value + " Count: " + x.Count);

}