Check if Exists and if so, Add it to Other List

Question

Hi there! I've just experienced an odd issue and I'd like to be enlightened on this topic.

I'm posting a piece of code in which I'm inside a switch, but that's not so important; what matters is that I'd like to check if in the list called mirror exists one object with a certain value and if so, add it immediately to a second list called Lpositions.

Since I'm already checking if something like that exists it would be awesome to be able to just address that " x" and say: Lpositions.Add(x.position)! but that returns an error... how sad.

Could you help me?

I'm self-teaching me C# so if you could elaborate a bit your answer or pass me a link of not-too-complicated code I'd really appreciate.

Thanks for your time!

 //Check if something other than rand is empty in our mirror list
             case 2:
 
                 //hypotheticalActorsOnPoint is the value I want to check 
                 if(mirror.Exists(x => x.hypotheticalActorsOnPoint == 0)){
                     
                     for(int j = 0; j < mirror.Count; j++){
                         
                         if(mirror[j].hypotheticalActorsOnPoint == 0){
                             
                             Lpositions.Add(mirror[j].position);
                             mirror[j].hypotheticalActorsOnPoint++;
                             i++;                //this code is inside a while loop too
                             
                             if(mirror[j].isFull){
                                 
                                 mirror.Remove(mirror[j]);
                             }
                             
                             break;
                         }
                     }
 
                     break;
                 }
 
                 else{
 
                     goto default;
                 }

Answer 1

Best Answer

Answer by Mapleman · Apr 21, 2015 at 06:22 AM

Instead of using Exists, you could use Find. Something like this:

 case 2:
    var t = mirror.Find(x => x.hypotheticalActorsOnPoint==0);
    if (t!=null)
    {
        Lpositions.Add(t.position);
        ...
    }

Your question about why you can't use 'x' inside your if statement is bit more complex though. What C# lambda syntax means in your case goes roughly like follows:

The statement below is actually instruction to compiler to generate an anonymous method which takes in one parameter of type x and returns boolean.

x => x.hypotheticalActorsOnPoint == 0

if you had a method with signature: bool MyComparer(T elementInList)

where T is the type of your object stored in list, you could write your if statement like this:

if(MyComparer) { ... }

If you check the msdn documentation for example the Find method I proposed you could use, it's signature is like:

public T Find( Predicate match )

And as it happens the Exists method has exactly the same signature:

public bool Exists( Predicate match )

So keep in mind that whenever you are writing a lambda expression, you are actually declaring a method.

Hope this clarifies things a bit for you.

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esitoinatteso · Apr 21, 2015 at 11:16 AM 0

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Awesome!!! Yes that's exactly what I wanted to do, thanks a lot both for the code and the valuable tips about lambdas, I'm starting to understand them a bit more!

Check if Exists and if so, Add it to Other List

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