C# remove duplicates from jagged array

Question

I am writing an algorithm for university. And I have almost everything except the last thing. I now have jagged array of numbers, example of this array:

[0][1]
[1][11,12]
[2][3,7,11,15]
[3][6,7,10,11]

And i need to remove duplicates, like delete every number from all next rows, that is present in the previos row. Output should be something like this:

[0][1]
[1][11,12]
[2][3,7,15]
[3][6,10]

I have tried something like this:

for (int i = 0; i <= numbers.Length + 1; i++)
{
    int size = numbers[i].Length;
    for (int j = 0; j < size; j++)
    {
        if (numbers[i][numbers[i].Length] != numbers[i + 1][numbers[i + 1].Length])
        {
            newNumbers[i][j] = numbers[i][j];
        }
    }
}

But it does not work the way it should.

It's the if statement and the contents within if statement that is causing issue. Make sure you make correct use of i and j variable to manipulate array. — SwapnilGhodke
– SwapnilGhodke, Commented Jan 12, 2020 at 9:52
You may need to have a secondary data structure (such as a dictionary) which stores the duplicate number and it’s locations. Your first pass of the array populates this dictionary- the second pass uses this information to remove duplicates — auburg
– auburg, Commented Jan 12, 2020 at 9:56

Pavel Anikhouski · Accepted Answer · 2020-05-23 12:20:10Z

3

You can solve it by using Except method from System.Linq namespace.

At every loop iteration go through all next rows and get the difference between these rows and current one and reassign it back. It's possible, because jagged array is an array whose elements are arrays and you have the same int data type for all items

int[][] jaggedArray = new int[4][];

jaggedArray[0] = new[] { 1 };
jaggedArray[1] = new[] { 11, 12 };
jaggedArray[2] = new[] { 3, 7, 11, 15 };
jaggedArray[3] = new[] { 6, 7, 10, 11 };

for (int i = 0; i < jaggedArray.Length; i++)
{
    var currentRow = jaggedArray[i];
    for (int j = i + 1; j < jaggedArray.Length; j++)
    {
        var result = jaggedArray[j].Except(currentRow);
        jaggedArray[j] = result.ToArray();
    }
}

If you print the result array

foreach (var array in jaggedArray)
{
    foreach (var item in array) 
        Console.Write($"{item} ");

    Console.WriteLine();
}

The output will be the following

edited May 23, 2020 at 12:20

answered Jan 12, 2020 at 9:55

Pavel Anikhouski

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3 Comments

auburg Over a year ago

Would that work if there’s duplicate numbers in non adjacent rows?

Pavel Anikhouski Over a year ago

OP mentioned that delete every number from all next rows, that is present in the previos row. The internal for loop go through all next rows until end of array, at every iteration of main loop

Jolof Over a year ago

@PavelAnikhouski it's working, thank you very much. You just saved me from sitting next few hours and trying to achive this.

Peter Petukhov · Accepted Answer · 2020-01-13 11:25:53Z

1

public static int[][] RemoveDuplicates(this int[][] data)
{
    var result = new int[data.Length][];
    var used = new List<int>();

    for (int i = 0; i < data.Length; i++)
    {
        var hashSet = new HashSet<int>(data[i].Except(used));
        result[i] = hashSet.ToArray();
        used.AddRange(hashSet);
    }
    return result;
}

answered Jan 13, 2020 at 11:25

Peter Petukhov

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