C# learning related series of Linq usage---where and select usage (2)

1. Select usage

The select in Linq allows us to easily operate on each item in the List and generate a new list.

var tt=list.select(p=>p+10);
//select括号内为List中的每一项，p+10即为对每一项的操作，即对每项都加10生成新的List

Usage examples:

1. Lambda expression

int[] array = { 1,5,6,7,6,9,12,2,7,6,33};
List<int> l1 = new List<int>(array);
var t1 = l1.Select((p)=>p+10);
foreach (var item in t1)
{
     Console.WriteLine(item);
}

The output is:

2. Linq syntax

            List<Student_1> stuList = new List<Student_1>()
            {
                new Student_1(){ID=1,Name="John",Chinese=92,Math=88,English=92},
                new Student_1(){ID=2,Name="Mary",Chinese=87,Math=94,English=82},
                new Student_1(){ID=3,Name="KangKang",Chinese=89,Math=91,English=96},
                new Student_1(){ID=4,Name="Maria",Chinese=88,Math=65,English=94},
                new Student_1(){ID=5,Name="Ben",Chinese=70,Math=91,English=82},
            };

            var t1 = from e in stuList select e.English;
            foreach (var item in t1)
            {
                Console.WriteLine(item);
            }

2. SelectMany usage

In C# Linq, the SelectMany method is used to convert each element in a collection to another collection and merge all converted collections into one collection.

List<List<int>> list = new List<List<int>>()
{
    new List<int>() { 1, 2, 3 },
    new List<int>() { 4, 5, 6 },
    new List<int>() { 7, 8, 9 }
};

var result = list.SelectMany(x => x);

foreach (var item in result)
{
    Console.WriteLine(item);
}

3. Where usage

where in Linq mainly filters data and generates a new List.

            List<Student_1> stuList = new List<Student_1>()
            {
                new Student_1(){ID=1,Name="John",Chinese=92,Math=88,English=92},
                new Student_1(){ID=2,Name="Mary",Chinese=87,Math=94,English=82},
                new Student_1(){ID=3,Name="KangKang",Chinese=89,Math=91,English=96},
                new Student_1(){ID=4,Name="Maria",Chinese=88,Math=65,English=94},
                new Student_1(){ID=5,Name="Ben",Chinese=70,Math=91,English=82},
            };
            
            //lambda表达式 表达式内部填的是判断条件
            var t1 = stuList.Where(p => p.English == 88);
            // Linq 语句
            var t1 = from e in stuList where e.English == 82 select e;

It should be noted that the Lambda expression does not need to end with select, but the Linq statement must end with select or an error will be reported.

The running result is:

references:

C#'s LINQ select query, where filtering, group grouping, join association_c# t.select().join_Xiaolong's blog in Shandong-CSDN blog