Sort dictionay with duplicate values of array

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Hello i have below dict. & i have to sort this based on duplicate value of double[] so am looking for sorted list with all duplicates only

C#

Dictionary<int, double[]> counts1 = new Dictionary<int,double[]>();

Am trying to use this but it doesn't work out

C#

var duplicateValues = counts1.GroupBy(x => x.Value).Where(x => x.Count()> 1);

any leads appreciated thanks

What I have tried:

sort duplicate array values in dictionary

below is the dictionary

C#

Dictionary<int, double[]> counts1 = new Dictionary<int,double[]>();

below method trying to sort out

C#

var duplicateValues = counts1.GroupBy(x => x.Value).Where(x => x.Count()> 1);

Posted 24-Mar-24 23:23pm

Member 14224038

Updated 24-Mar-24 23:38pm

Richard Deeming

v3

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Graeme_Grant 25-Mar-24 5:34am

post some sample data that needs to be sorted

3 solutions

Solution 3

I'm not sure what you want to achieve, but...
Suppose you want to sort dictionary values based on its occurence.

Here is an example:

C#

Dictionary<int, double[]> d = new Dictionary<int,double[]>()
{
	{1, new double[]{.5, 1.2, 3.4, .5, 1.2, 3.4, .5, 1.2, 3.4, .5, 1.2}},
	{2, new double[]{.5, 1.2, 3.4, .5, 1.2, 3.4, .5, 1.2, 3.4, .5, 1.2, 3.4, 3.4}},
	{3, new double[]{.5, 1.2, 3.4, .5, 1.2, 3.4}},
	{4, new double[]{.5, 1.2, 3.4, 3.4, 3.4, .5, 1.2, 3.4, .5, 3.4}},
	{5, new double[]{.5, 1.2, 3.4}}
};


Dictionary<int, Dictionary<double, int>> result = d
	.Select(x=> new KeyValuePair<int, Dictionary<double, int>>
		(x.Key, new Dictionary<double, int>(x.Value.GroupBy(y => y)
				.Select(g => new KeyValuePair<double, int>(g.Key, g.Count()))
				.OrderByDescending(k => k.Value)
				.ToDictionary(kvp => kvp.Key, kvp => kvp.Value))))
	.ToDictionary(kvp => kvp.Key, kvp => kvp.Value);

Result:

Key    Values
1      0.5 | 4 
       1.2 | 4 
       3.4 | 3 
2      3.4 | 5 
       0,5 | 4 
       1,2 | 4 
and so on...

Posted 26-Mar-24 23:39pm

Maciej Los

Solution 4

Hi,

refer this article will help you
Using Lookup For Duplicate Key Value Pairs Dictionary[^]

Posted 27-Mar-24 2:20am

Manoj B. Kalla

Updated 27-Mar-24 3:19am

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Richard Deeming · Accepted Answer · 2024-03-24T23:47:00

Solution 1

In .NET, arrays are only considered "equal" if they are the same reference. Two different arrays containing the same values are not considered equal.

If you need to find duplicates amongst different arrays containing the same values, you'll need a custom equality comparer.

C#

public sealed class ArrayEqualityComparer<T> : IEqualityComparer<T[]>
{
    private readonly IEqualityComparer<T> _elementComparer;
    
    public ArrayEqualityComparer(IEqualityComparer<T> elementComparer)
    {
        _elementComparer = elementComparer ?? throw new ArgumentNullException(nameof(elementComparer));
    }
    
    public ArrayEqualityComparer()
    {
        _elementComparer = EqualityComparer<T>.Default;
    }
    
    public int GetHashCode(T[] obj)
    {
        if (obj is null || obj.Length == 0) return 0;
        
        HashCode code = new HashCode();
        for (int index = 0; index < obj.Length; index++)
        {
            T element = obj[index];
            code.Add(element, _elementComparer);
        }
        
        return code.ToHashCode();
    }
    
    public bool Equals(T[] x, T[] y)
    {
        if (x is null) return y is null;
        if (y is null) return false;
        if (x.Length != y.Length) return false;
        
        for (int index = 0; index < x.Length; index++)
        {
            T xElement = x[index];
            T yElement = y[index];
            if (!_elementComparer.Equals(xElement, yElement))
            {
                return false;
            }
        }
        
        return true;
    }
}

You will then need to pass an instance of that equality comparer to the GroupBy method:

C#

var duplicateValues = counts1.GroupBy(x => x.Value, new ArrayEqualityComparer<double>()).Where(x => x.Count()> 1);

Posted 24-Mar-24 23:47pm

Richard Deeming

Updated 25-Mar-24 3:00am

v3

Comments

M-Badger 25-Mar-24 6:47am

Should the GetHashCode method have a 'return code' line or does the compiler know what to do with that ?

Richard Deeming 25-Mar-24 6:49am

Good spot! return code.ToHashCode(); added.

Member 14224038 25-Mar-24 8:50am

thanks a lot for the code, but it doesnt workout for me. dont know why
while debug itonly goes to public ArrayEqualityComparer()
{
_elementComparer = EqualityComparer<t>.Default;
}

& return back with null. my double values have array of 6.

Richard Deeming 25-Mar-24 8:58am

What does "return back with null" mean?

Richard Deeming 25-Mar-24 9:19am

I've just tried the code, and it works as expected:
Duplicate Arrays | C# Online Compiler | .NET Fiddle[^]

Member 14224038 26-Mar-24 4:07am

Hi richard, dont know while debug i can only see instance of public ArrayEqualityComparer()
{
_elementComparer = EqualityComparer<t>.Default;
} being called, but the methods bool Equals & GetHashCode are not called, sorry am pretty new to c#

Member 14224038 26-Mar-24 6:08am

my double values are like below
-9.6120821264220819.850847808492751.720462149016156.249866832965873.0267377131468160.065082033597
-9.612082126422119.850847808492751.720462149016156.249866832965873.0267377131468160.065082033597
-2554-522510448

so here first & second are same & list should filtered with these two.
when i try to debug
from here
var duplicateValues = counts1.GroupBy(x => x.Value, new ArrayEqualityComparer<double>()).Where(x => x.Count() > 1);

it goes to here
public ArrayEqualityComparer()
{
_elementComparer = EqualityComparer<t>.Default;
} it is returned as null as a filtered list in duplicateValues variable

Richard Deeming 26-Mar-24 6:32am

Those don't look like valid double values - you've got three values, two with multiple decimal points, and one with multiple minus signs.

Even assuming that's just a formatting error, none of the three lines you provided could be considered "equal", so there should not be any duplicates returned. The first two are close, but 22081 is clearly not equal to 2211.

Also, bear in mind that double is an approximate type. Two values which look equal when you print them out may not actually be equal for comparison. The general recommendation is to check whether the difference between the values is "small enough" for your purposes.

That would mean passing a custom element equality comparer to the ArrayEqualityComparer class:

public class DoubleEqualityComparer : IEqualityComparer<double>
{
    private readonly double _epsilon;
    
    public DoubleEqualityComparer(double epsilon)
    {
        if (double.IsNaN(epsilon) || double.IsInfinity(epsilon)) throw new ArgumentOutOfRangeException();
        _epsilon = Math.Abs(epsilon);
    }
    
    public DoubleEqualityComparer()
    {
        _epsilon = double.Epsilon;
    }
    
    public int GetHashCode(double obj) => 0; // See note
    public bool Equals(double x, double y) => Math.Abs(x - y) <= _epsilon;
}

var duplicateValues = counts1.GroupBy(x => x.Value, new ArrayEqualityComparer<double>(new DoubleComparer(1E-12))).Where(x => x.Count() > 1);

* Note: It is not possible to provide a proper GetHashCode implementation for this case; the DoubleEqualityComparer already breaks the implicit requirements of the equality comparer, which requires that Equals(x, y) == true and Equals(y, x) == true means that Equals(x, z) == true. If you have y = x + epsilon and z = y + epsilon, then Equals(x, y) == true and Equals(y, z) == true, but Equals(x, z) == false.

As a hacky workaround, this implementation returns 0 as the hash-code for every value, which forces them all into the same "bucket". That means that "close enough" values will be considered equal, but will have an impact on the performance of any hashtable-like structure that uses this comparer.

Member 14224038 26-Mar-24 7:23am

Sorry my bad they are like this,
-9.612082126422081 , 9.85084780849275 , 1.72046214901615 , 6.24986683296587 ,3.026737713146816, 0.065082033597
-9.612082126422081, 9.85084780849275 , 1.72046214901615 , 6.24986683296587, 3.026737713146816, 0.065082033597
-3.21208212642211, 2.26084780849275 , 1.72046214901615 , 9.24986683296587, 2.026737713146816, 0.065082033597

so first & 2nd are exact match. Maybe if i can round upto 4 decimal places will it work then ?Å

Richard Deeming 26-Mar-24 7:40am

Well those numbers work fine even without the custom element comparer:
Duplicate Arrays | C# Online Compiler | .NET Fiddle[^]

Member 14224038 26-Mar-24 8:35am

Doesnt work for me with below numbers
27.1879476277225 37.5134291710464 73.6017562082174 93.0498965871104 90.6893190757005 181.946376092798
27.1879476277225 37.5134291710464 73.6017562082174 93.0498965871104 90.6893190757005 181.946376092798
-25 54 -52 25 104 48
I debug the code it goes inside the sealed class & returns from below
public ArrayEqualityComparer()
{
_elementComparer = EqualityComparer<t>.Default;
}
it doesnt go inside gethashcode or bool methods ?

Richard Deeming 26-Mar-24 8:47am

Those numbers work fine for me:
[Fork] Duplicate Arrays | C# Online Compiler | .NET Fiddle[^]

So what are you doing differently?

Member 14224038 26-Mar-24 8:49am

but do i need to call Gethashcode or bool methods externally or below line is enough
var duplicateValues = counts1.GroupBy(x => x.Value, new ArrayEqualityComparer<double>()).Where(x => x.Count() > 1);

Richard Deeming 26-Mar-24 8:50am

Again, look at the sample link I provided. GroupBy will take care of calling those methods; you just need to pass the equality comparer instance into that method.

Member 14224038 26-Mar-24 8:57am

ohk & what will be best way to get filtered list of count1 with only repitative elmenets, i mean the one which is not repitative (double array)can be filtered out

Richard Deeming 26-Mar-24 9:00am

The phrase "extracting blood from a stone" springs to mind! 🤦‍♂️

You already have the code to do that. I have given you a link to a demo which shows it working.

So what are you doing differently to make it "not work"?

Just repeatedly saying "it doesn't work" is not helpful.

Member 14224038 26-Mar-24 9:04am

yes it works now thanks it was my mistake

Member 14224038 26-Mar-24 9:08am

Just wondering if you can help me to filter this list ?to keep only duplcate values ? am checking count1.remove() it says remove values with specified key so should i loop above values & check all 6 array elements & use this method ?

Richard Deeming 26-Mar-24 9:22am

So something like this?

IEnumerable<int> duplicateKeys = counts1
    .GroupBy(x => x.Value, new ArrayEqualityComparer<double>())
    .Where(x => x.Count() > 1)
    .SelectMany(g => g).Select(i => i.Key);

List<int> keysToRemove = counts1.Keys.Except(duplicateKeys).ToList();

foreach (int key in keysToRemove)
{
    counts1.Remove(key);
}

[Fork] [Fork] Duplicate Arrays | C# Online Compiler | .NET Fiddle[^]

Member 14224038 26-Mar-24 9:39am

yes something like this but above code doesnt work i dont know if i need groupby method anymore. but i need at last list of keyvalues where values are duplicate array of double, sorry for all this mess but thanks for helping me out

Richard Deeming 26-Mar-24 9:42am

OK, image you're driving your car, and you break down. You pick up the phone, call the garage, say "It doesn't work!", and then hang up. How soon do you think the mechanic will arrive with precisely the right part to fix the problem?

Back to your question. Remember, we cannot see your screen, access your computer, or read your mind. All we have to go on is what you type in this little box right here.

So how helpful do you think it is to keep saying "it doesn't work", despite having an online code sample where it clearly does work, without providing any further information?

Help us to help you. Stop saying "it doesn't work", and start explaining precisely what the problem is, and what you are doing differently to the sample provided!

Member 14224038 26-Mar-24 9:55am

Ok i try to debug i got below error after it goes below line
List<int> keysToRemove = counts1.Keys.Except(duplicateKeys).ToList();
Could not load file or assembly 'Microsoft.Bcl.HashCode, Version=1.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51' or one of its dependencies. The system cannot find the file specified.'

Richard Deeming 26-Mar-24 9:56am

Then you'll need to add a NuGet reference to the Microsoft.Bcl.HashCode[^] package.

Member 14224038 26-Mar-24 10:12am

that i can see is already there in reference, i will try more thanks

Maciej Los 25-Mar-24 13:26pm

5ed!

George Swan 26-Mar-24 5:21am

Excellent 5ed!