如何从 lambda 的列表中获取一种类型的孩子？

Question

Here is the code:

private struct Child {
        public string A;
        public string B;
        public boolean C;
}
List<Child> Test=new List<Child>();

Now I want to get all the string A from the List<Child> Test .

I have to do it like this yet:

List<string>NewList=new List<string>();
foreach(Child C in Test)
{
NewList.Add(C.A);
}

It is so troublesome that I wanna whether there is a way faster, for example by using the lambda?

Thank you.

Answer 1

var NewList = Test.Select(x => x.A).ToList();

but this is not faster, only a little less code.

Answer 2

As mentioned in this Answer: https://stackoverflow.com/a/1178913/3121280

you can do it like this:

NewList = Test.Select(
    x => x.A 
).ToList();

Answer 3

Select shown by others is what you need here, but it's worth mentioning SelectMany for the moments where you need granchildren.

private class Child
{
    public string Name { get; set; }
    public List<Child> Children { get; set; }
}

public static void Main()
{
    var children = new List<Child>(){
        new Child{
            Name = "C1",
            Children = new List<Child>{
                new Child{ Name = "C1_C1"},
                new Child{ Name = "C1_C2"}
            }},
        new Child{
            Name = "C2",
            Children = new List<Child>{
                new Child{ Name = "C2_C1"},
                new Child{ Name = "C2_C2"}
            }}
        };

    var granchildren = children.SelectMany( c => c.Children);

    Console.WriteLine(string.Join(", ", granchildren.Select(c => c.Name)));
}

The snippet above outputs the following:

C1_C1, C1_C2, C2_C1, C2_C2