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Generics - List.Exists Method

Posted on 2006-07-04
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Last Modified: 2008-03-17
Hello,

I am very new to generics and looking for an example showing how to use the List.Exists delegate. I want to search a particular list to see if an item exists in it.  If the item doesn't exist, I want to add it to another list (I'm trying to test for duplicates).

I'm trying to do something like this (I know the syntax is incorrect.):

foreach (myListItem item in myItemList
{
     if (!returnedItemList.Exists(item) // not sure of syntax here
    {
         newList.Add(item);
    }
}


How would I perform this check using the Predicate delegate?

Thanks!
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Question by:marmaxx
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5 Comments
 
LVL 44

Expert Comment

by:bruintje
ID: 17040293
Hi marmaxx,
----------

funny a likewise question was blogged here
http://channel9.msdn.com/ShowPost.aspx?PostID=76961

not sure about it but in that instance the Contains function was needed is that what you need?

foreach (myListItem item in myItemList
{
     if (!returnedItemList.Contains(item)
    {
         newList.Add(item);
    }
}

----------
bruintje
share what you know, learn what you don't
0
 

Author Comment

by:marmaxx
ID: 17040360
Hi bruintje,

No, unfortunately I can't use the Contains method. The program I am working with uses a different implementation of contains (passing in an object reference rather than a value). Of course, I might not be explaining this very well, since I'm only just starting with generics. Either way, I've go to figure out how to do this using Exists, with the Predicate.
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Accepted Solution

by:
bruintje earned 500 total points
ID: 17040392
that was added later in the same blog entry

2 ways actually, the first one using the predicate delegate

and another one

--
foreach( string s in returnedItemList )
{

    bool found = returnedItemList.Exists( delegate(string t) { return item == t; } );

    if( !found) { newList.Add( item ); }
}
--

hope this helps a bit more
0
 

Author Comment

by:marmaxx
ID: 17043625
Nope, couldn't get the example to work.

What I am trying to do is compare two Lists: List1 and List2. I want to loop through each item of List1 to determine if it exists in List2. If it does, I want to add it to another list. Each of the list items has an ID property, which I need to convert to string, and compare.

I wasn't able to figure out how to do this using the example.
0
 

Author Comment

by:marmaxx
ID: 17146642
I was able to get this to work with a little 'tweak' here and there. Thanks for the help!
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