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List<> split in 2

Posted on 2009-05-12
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Last Modified: 2013-12-17
I have a Generic List (List<>).
I want to split it into 2 Lists. In the first one go items which indexnumber is an even number (0,2,4...)
and in the second items which indexnumber is an odd number (1,3,5...).
How is best to do that?
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Question by:johnkainn
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8 Comments
 
LVL 16

Expert Comment

by:Walter Ritzel
ID: 24366152
The first way I can think of is running thru the list and according to the index, adding in the odd or the even list.
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Expert Comment

by:p_davis
ID: 24366183
List<YourObject> evenResults = mainList.FindAll(x=>x.IndexNumber % 2 == 0 || x.IndexNumber == 0);
List<YourObject> oddResults = mainList.Findall(x=>x.IndexNumber % 2 > 0);

maybe?
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Expert Comment

by:Walter Ritzel
ID: 24366314
The only problem with this approach is that you depend upon using a property from the object inside the list to make the decision.
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Expert Comment

by:p_davis
ID: 24366357
umm that's what the asker is basing the branching (separate lists) on. unless i am misunderstanding the question/purpose.
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Expert Comment

by:p_davis
ID: 24366369
and why would that be a problem? i am asking seriously b/c i am always willing to learn something new.
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Accepted Solution

by:
Walter Ritzel earned 125 total points
ID: 24366400
This would be the standard way:
<eeSnippet>
    class SimpleObject
    {
        private int id;
        private String name;

        public String Name
        {
            get { return name; }
            set { name = value; }
        }

        public int Id
        {
            get { return id; }
            set { id = value; }
        }

        public SimpleObject(int p_id, String p_name)
        {
            this.id = p_id;
            this.name = p_name;

        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            //Creating and Populating the list
            List<SimpleObject> mainList = new List<SimpleObject>();
            for (int i=0; i < 10; i++)
            {
                mainList.Add(new SimpleObject(i,"name " + i.ToString()));
            }

            //Approach not using LINQ
            List<SimpleObject> oddList = new List<SimpleObject>();
            List<SimpleObject> evenList = new List<SimpleObject>();
            int j = 0;
            foreach(SimpleObject obj in mainList)
            {
                if ((j % 2 == 0) || (j == 0))
                {
                    evenList.Add(obj);
                }
                else
                {
                    oddList.Add(obj);
                }
            }
        }
    }
</eeSnippet>
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LVL 22

Assisted Solution

by:p_davis
p_davis earned 125 total points
ID: 24366411
that effectively does the exact same thing that i posted.
0
 
LVL 16

Expert Comment

by:Walter Ritzel
ID: 24366609
Sure, man. Let me explain: it's become a problem if, for example, your object does not have an IndexNumber or any number property... My solution does not consider the values inside the object, just the position inside the list.
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