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How can I remove all null elements from an array object[,] in C#. I've already seen the similar question in StackOverflow : Remove blank values in the array using c#

The problem is they are using a method called Where() to solve the problem with a simple array type object[], but I'm dealing with an array type object[,] and there is unfortunately no method Where() implemented for this class. For example :

object[,] data = new object[2,2]{{null,null},{1,2}};

Then, data contains : 

[0, 0] [object]:null
[0, 1] [object]:null
[1, 0] [object]:1
[1, 1] [object]:2

As you can see (in my specific case), if one element is null then all the row of this element is null. I would like to get :

[0, 0] [object]:1
[0, 1] [object]:2

Any help ?

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2 Answers 2

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Well there is no LINQ Where for two dimensional arrays. If you can change your array definition to be an object[][] you can use a foreach to iterate through the "rows" and filter out rows that have all nulls.

public class RemoveNulls
{
    [Test]
    public void RemoveNullItems()
    {
        var items = new object[][] { new object[] { null, null }, new object[] { 1, 2 } };
        var cleanRows = new List<object[]>();
        foreach (object[] row in items)
        {
            var newRow = row.Where(item => item != null).ToArray();
            if (newRow.Any()) cleanRows.Add(newRow);
        }
        var result = cleanRows.ToArray();
    }
}
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7 Comments

Hi, thanks for your answer. Did you already test your code ? I'm having an error at the line :var newRow = row.Where(item => item != null).ToArray(); The exception is : System.ArgumentNullException: 'Value cannot be null. Parameter name: source'
This is normal, since the variable row is null at his first occurence.
IList<object[]> cleanRows = Enumerable.Empty<object[]>().ToList();? Is that just var cleanRows = new List<object[]>();?
@BoubacarTraoré Unfortunately I was thinking of an array of arrays rather than a two-d array. I'll delete for now until I can fix it.
@Ry- yes it is, nice catch
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The approach is as follows:

  • Count how many rows you would like to remove
  • Create an array of the appropriate size
  • Copy rows that you would like to keep

Use a helper method to detect rows with a null:

static bool RowHasNull(object[,] data, int row) {
    return Enumerable.Range(0, data.GetLength(1)).Any(c => data[row,c] == null);
}

Now the implementation would look like this:

var oldRowCount = data.GetLength(0);
var newRowCount = oldRowCount - Enumerable.Range(0, oldRowCount).Count(r => RowHasNull(data, r));
if (newRowCount == 0) ... // the array is empty, do something about it - e.g. throw an exception
var res = new object[newRowCount, data.GetLength(1)];
int r = 0;
for (var row = 0 ; row != oldRowCount ; row++) {
    if (RowHasNull(data, row)) {
        continue;
    }
    for (int c = 0 ; c != data.GetLength(1) ; c++) {
        res[r,c] = data[row, c];
    }
    r++;
}
return res;
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3 Comments

Also if “if one element is null then all the row of this element is null” is true then RowHasNull can be data[row, 0] == null. (Is that Enumerable.Range parenthesis in the right spot?)
@Ry- Right, the parenthesis was in a wrong spot. You are also right about data[row,0] but since adding a little generalization "costs" only one line of code, I figured I might as well do it.
Awesome ! Thank you very much, this solved my issue ! You should also correct your second line : var newRowCount = oldRowCount - Enumerable.Range(0, rowCount).Count(r => RowHasNull(data, r)); As you can see the variable rowCount doesn't exist. I guess you mean oldRowCount

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