automatically sorting data structure for objects based on key?

Question

I would like a structure to automatically sort data for me based on an associated key, but once this is done I never have to grab any of the objects with the key, I just want to take the first one off the list. In my specific case each object has an associated float value, and I want to order them from low to high.

For example I want to be able to sort a list of integers, but by their corresponding float 'keys' and grab the one at index 0 - (which will be the one with the lowest associated float)

I came across orderedDictionary's but I don't fully understand them and don't know how appropriate they are for my needs. I thought they were just a dictionary that allowed you to also index into them, but they aren't a template class?

What don't you understand about SortedList and OrderedDictionary? You have not explained your use case completely. — Oded
– Oded, Commented Jun 7, 2012 at 18:19
So if you have a bunch of <int,float> pairs, you want to sort by the float but also have fast access by int, right? — SirPentor
– SirPentor, Commented Jun 7, 2012 at 18:23
Yes I will be adding new items, but I don't need to access by int - just grab the one with the lowest associated float value. — Dollarslice
– Dollarslice, Commented Jun 8, 2012 at 7:13

Jf Beaulac · Accepted Answer · 2012-06-08 14:29:10Z

3

You probably want a SortedSet: http://msdn.microsoft.com/en-us/library/dd412070.aspx

If you are not using .net 4.0, its available in the PowerCollection project: http://powercollections.codeplex.com/

Example with .Net4.0 SortedSet

SortedSet<float> set = new SortedSet<float>( );
set.Add(13.3f);
set.Add(0.5f);
set.Add(5.5f);

Console.WriteLine(string.Format("Minimum Value: {0}", set.Min)); // prints 0.5
Console.WriteLine(string.Format("Maximum Value: {0}", set.Max)); // prints 13.3

foreach (float f in set)
{
    Console.WriteLine(f);
}
// prints:
// 0.5
// 5.5
// 13.3

// using custom IComparer<float>, see implementation below
set = new SortedSet<float>(new FloatDescComparere());

set.Add(13.3f);
set.Add(0.5f);
set.Add(5.5f);

Console.WriteLine(string.Format("Minimum Value: {0}", set.Min)); // prints 13.3
Console.WriteLine(string.Format("Maximum Value: {0}", set.Max)); // prints 0.5

foreach (float f in set)
{
    Console.WriteLine(f);
}
// prints:
// 13.3
// 5.5
// 0.5

Desc IComparer:

private class FloatDescComparere : IComparer<float>
{
    public int Compare(float x, float y)
    {
        if (y > x)
            return 1;
        else if (x > y)
            return -1;
        else
            return 0;
    }
}

edited Jun 8, 2012 at 14:29

answered Jun 7, 2012 at 18:22

Jf Beaulac

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2 Comments

Dollarslice Over a year ago

Can you explain what they are a little?

Jf Beaulac Over a year ago

I Added a little example on how to use the SortedSet from .NET4.0

Mark · Accepted Answer · 2012-06-07 18:22:56Z

0

You can use a hash table http://en.wikipedia.org/wiki/Hash_table, put the 'key' in the hash and search your element 'key' in the hash , if the hash has the key the you have that element . You must update each time you add a new element O(1) but you also have a find complexity of O(1).

answered Jun 7, 2012 at 18:22

Mark

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1 Comment

Mark Over a year ago

I totally forgot about that he wanted to be sorted , i answered just for the finding part. Then just sort the elements and apply the hash.

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