Using LINQ and lambdas to search Dictionary>Class>

问题:

given the following data source:

public struct Strc
{
    public decimal A;
    public decimal B;
    // more stuff
}

public class CLASS
{
    public List<Strc> listStrc = new  List<Strc>();
    // other stuff
}

Dictionary<string, CLASS> dict = new Dictionary<string, CLASS>();

I need to collect all the Strc.B in the dictionary, provided Strc.A is e.g > 3.

I get the result doing the following:

List<decimal> results = (
    from v in dizS.Values
    from ls in v.listStr
    where ls.A > 3
    select ls.B
    ).ToList();

I was also trying to write it using lambdas, but I fail miserably...

var res = dict.Values.Where(x => x.listStrc.Any(z => z.A > 3))

this is as far as I could get, but I do not manage to select then the .B data... What do I do wrong? (given I did anything right in the first place :D) Thanks for your time.

回答1:

You're essentially flattening to a sequence of the struct values - and that flattening is represented with SelectMany. So you want:

var res = dict.Values
    .SelectMany(x => x.listSrc)
    .Where(ls => ls.A > 3)
    .Select(ls => ls.B);

This is basically equivalent to your query expression, but your attempted method calls suggest trying to get a different result, where if any of the entries of listSrc have an A value greater than 3, you'd want all of the B values from that listSrc. Hopefully the former is what you really want, but it's worth thinking about that carefully.

回答2:

You can try this

var result = dict.Values.SelectMany(x=>x.listStrc.Where(l=>l.A>3)).Select(x=>x.B);