Way to remove duplicate values from a list C#

Question

I have seen other people having a similar problem, but no solution has been able help me with mine.

I was looking for a way to make:

List<int> Factors = new List<int> {2, 5, 5, 7, 2, 3};

return:

{7, 3};

Is there any way that this can be done?

How is that removing duplicate values? what happened to 2, 5? — Vikas Gupta
– Vikas Gupta, Commented Nov 16, 2014 at 17:29
You may want to see the answer to this question: stackoverflow.com/questions/47752/… — Adam H
– Adam H, Commented Nov 16, 2014 at 17:29
@VikasGupta, OP want's only those number which have only one appearance. — Rahul
– Rahul, Commented Nov 16, 2014 at 17:32

Selman Genç · Accepted Answer · 2014-11-16 17:28:55Z

9

Using GroupBy you can group the numbers and get those groups that has only one number:

Factors = Factors.GroupBy(x => x)
   .Where(g => g.Count() == 1)
   .Select(g => g.Key)
   .ToList();

answered Nov 16, 2014 at 17:28

Selman Genç

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3 Comments

Rahul Singh Over a year ago

@Selamn22 - I don't think there's any need to filter. Factors.GroupBy(x => x).Select(x => x.Key).ToList(); will do.

Selman Genç Over a year ago

@RahulSingh that won't remove the duplicates. it will do exact same thing with Distinct.

Rahul Singh Over a year ago

@Selman22 - Oops Yes Got It! Misunderstood the question. +1 :-)

Rahul · Accepted Answer · 2014-11-16 18:02:33Z

0

Probably a Non LINQ solution. Add the numbers in list as key to the hashtable. in next iteration if the same key found in hashtable then increase it's corresponding value. so, at end you will remain with only those numbers which have only one appearance.

    static void Main(string[] args)
    {
        List<int> Factors = new List<int> { 2, 5, 5, 7, 2, 3, 2, 9, 8, 9, 11, 9, 12, 9, 13, 9 };
        Hashtable ht = new Hashtable();
        foreach (var item in Factors)
        {
            if (ht.ContainsKey(item))
            {
                ht[item] = Convert.ToInt32(ht[item]) + 1;
            }
            else
                ht.Add(item, 1);
        }

        foreach (var item in ht.Keys)
        {
            if (Convert.ToInt32(ht[item]) == 1)
            Console.WriteLine(item.ToString());
        }
    }

edited Nov 16, 2014 at 18:02

answered Nov 16, 2014 at 17:42

Rahul

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2 Comments

fejesjoco Over a year ago

This code only removes elements which occur an even number of times. It will leave elements which occur 1, 3, 5 etc times.

Rahul Over a year ago

@fejesjoco, what about now but thanks for pointing that. didn't think of that use case.

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