CODEWITHSUNDEEP
c#data-structuresmemory-managementwhile-loophashset
yamini
yamini

Reputation: 41

Hashset in c# is giving a strange behavior

I have a problem with HashSet in C#....

this is my code:

  List<int> elements = new List<int>();
        for(int i = 0;i< 100000;i++)
        {
            elements.Add(i);
        }
        HashSet<int> c = new HashSet<int>();
        foreach(var ele in elements)
        {
        c.Add(ele);
        }

        Console.WriteLine("Working HashSet " + c.Count);

        var Numbers = new HashSet<int>();
        var mycount = 0;
        using (TextReader reader = File.OpenText(@"myfile.txt"))
        {
            while ((line = reader.ReadLine()) != null)
            {
                mycount++;
                int parsed = int.Parse(line);
                Numbers.Add(parsed);
            }
        }

        Console.WriteLine("my counter took" + mycount);

        Console.WriteLine("Bad HashSet" + Numbers.Count);

Working HashSet 100 000

my counter took 500 000

Bad HashSet 9999

why the second hashset is not adding 500 000 items???? this is a mistery to me

Upvotes: 0

Views: 213

Answers (3)

Jon Hanna
Jon Hanna

Reputation: 113242

Presumably there're some duplicates. HashSet<T> represents a set, and provides set operations, hence the name. This is what we use it for.

Upvotes: 0

Robert Rouhani
Robert Rouhani

Reputation: 14678

A HashSet will not add duplicate numbers, because that's the way sets work.

For example, let's say these are the first few lines of myfile.txt:

1
2
3
1
2
3
4

You will be iterating over 7 values, but there are only 4 unique numbers in those lines, and HashSet will not add duplicates of 1, 2, or 3. In your case, you have 500,000 lines but only 9,999 unique numbers.

Upvotes: 5

Carra
Carra

Reputation: 17964

Your list contains 500.000 items of which there are 9999 unique.

Upvotes: 3

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