如何在LINQ中编写此代码块？

Question

I need to use linq as many times as possible and I have no idea how to use linq in this type of method.

I've tried some code from certain webs however none of them worked

List<MemorableD> memorables = new List<MemorableD>();
    List<StateMD> states = new List<StateMD>();
    void Find(List<MemorableD> selected)
    {
        for (int i = 0; i < states.Count; i++)
        {
            for (int j = 0; j < memorables.Count; j++)
            {
                if (states[i].Month == memorables[j].Month && states[i].Day == memorables[j].Day)
                {
                    MemorableD select = new MemorableD(memorables[j].Year, memorables[j].Month, memorables[j].Day, memorables[j].Event, states[i].Event);
                    selected.Add(select);
                }
            }
        }
    }

I need to write this add method with LINQ

Answer 1

Try to break down your problem. If you were to analyse your loops, you are iterating over the States and Memorables, and creating instances of MemorableD where State and Memorable have the same Month and Day and latter adding them to the List.

Translating it to Linq,

from StateMD state in states
from MemorableD memorable in memorables
    where state.Month == memorable.Month && state.Day == memorable.Day
let selectValue = new MemorableD(memorable.Year, memorable.Month, memorable.Day, memorable.Event, state.Event)
select selectValue

The second part of the problem is to add it to the List called selected. You can add an IEnumerable to selected using the AddRange method.

So, combining the Linq statement with AddRange method,

selected.AddRange(from StateMD state in states
                              from MemorableD memorable in memorables
                              where state.Month == memorable.Month && state.Day == memorable.Day
                              let selectValue = new MemorableD(memorable.Year, memorable.Month, memorable.Day, memorable.Event, state.Event)
                              select selectValue);