CODEWITHSUNDEEP
c#
paulio
paulio

Reputation: 393

IComparer for integers and force empty strings to end

I've written the following IComparer but I need some help. I'm trying to sort a list of numbers but some of the numbers may not have been filled in. I want these numbers to be sent to the end of the list at all times.. for example...

[EMPTY], 1, [EMPTY], 3, 2

would become...

1, 2, 3, [EMPTY], [EMPTY]

and reversed this would become...

3, 2, 1, [EMPTY], [EMPTY]

Any ideas?

        public int Compare(ListViewItem x, ListViewItem y)
    {
        int comparison = int.MinValue;
        ListViewItem.ListViewSubItem itemOne = x.SubItems[subItemIndex];
        ListViewItem.ListViewSubItem itemTwo = y.SubItems[subItemIndex];

        if (!string.IsNullOrEmpty(itemOne.Text) && !string.IsNullOrEmpty(itemTwo.Text))
        {
            uint itemOneComparison = uint.Parse(itemOne.Text);
            uint itemTwoComparison = uint.Parse(itemTwo.Text);

            comparison = itemOneComparison.CompareTo(itemTwoComparison);
        }
        else
        {
            // ALWAYS SEND TO BOTTOM/END OF LIST.
        }

        // Calculate correct return value based on object comparison.
        if (OrderOfSort == SortOrder.Descending)
        {
            // Descending sort is selected, return negative result of compare operation.
            comparison = (-comparison);
        }
        else if (OrderOfSort == SortOrder.None)
        {
            // Return '0' to indicate they are equal.
            comparison = 0;
        }

        return comparison;
    }

Cheers.

Upvotes: 3

Views: 3545

Answers (5)

Binary Worrier
Binary Worrier

Reputation: 51711

I'd actually approach this a completely different way, remove the empty slots, sort the list, then add the empty ones to the end of the list

static void Main(string[] args)
{
    List<string> ints = new List<string> { "3", "1", "", "5", "", "2" };
    CustomIntSort(ints, (x, y) => int.Parse(x) - int.Parse(y)); // Ascending
    ints.ForEach(i => Console.WriteLine("[{0}]", i));

    CustomIntSort(ints, (x, y) => int.Parse(y) - int.Parse(x)); // Descending
    ints.ForEach(i => Console.WriteLine("[{0}]", i)); 
}
private static void CustomIntSort(List<string> ints, Comparison<string> Comparer)
{
    int emptySlots = CountAndRemove(ints);
    ints.Sort(Comparer);
    for (int i = 0; i < emptySlots; i++)
        ints.Add("");
}
private static int CountAndRemove(List<string> ints)
{
    int emptySlots = 0;
    int i = 0;

    while (i < ints.Count)
    {
        if (string.IsNullOrEmpty(ints[i]))
        {
            emptySlots++;
            ints.RemoveAt(i);
        }
        else
            i++;
    }
    return emptySlots;
}

This question caught my attention recently, this comparer will do it either

class CustomComparer
    : IComparer<string>
{
    private bool isAscending;
    public CustomComparer(bool isAscending = true)
    {
        this.isAscending = isAscending;
    }
    public int Compare(string x, string y)
    {
        long ix = CustomParser(x) * (isAscending ? 1 : -1);
        long iy = CustomParser(y) * (isAscending ? 1 : -1);
        return ix.CompareTo(iy) ;
    }
    private long CustomParser(string s)
    {
        if (string.IsNullOrEmpty(s))
            return isAscending ? int.MaxValue : int.MinValue;
        else
            return int.Parse(s);
    }
}

Upvotes: 2

Amsakanna
Amsakanna

Reputation: 12954

else 
{ 
    //ALWAYS SEND TO BOTTOM/END OF LIST. 
    if (string.IsNullOrEmpty(itemOne.Text) && string.IsNullOrEmpty(itemTwo.Text)) 
    {
        return 0;
    }
    else if (string.IsNullOrEmpty(itemOne.Text)) 
    {
        return -1;
    }
    else if (string.IsNullOrEmpty(itemTwo.Text)) 
    {
        return 1;
    }
}

Upvotes: 0

Oded
Oded

Reputation: 499182

Always return 1 for your empty x values and -1 for your empty y values. This will mean that the comparer sees empty values as the greater value in all cases so they should end up at the end of the sorted list.

Of course, if both are empty, you should return 0 as they are equal.

Upvotes: 0

Dean Harding
Dean Harding

Reputation: 72668

Your logic is slightly off: your else will be entered if either of them are empty, but you only want the empty one to go to the end of the list, not the non-empty one. Something like this should work:

public int Compare(ListViewItem x, ListViewItem y)
{
    ListViewItem.ListViewSubItem itemOne = x.SubItems[subItemIndex];
    ListViewItem.ListViewSubItem itemTwo = y.SubItems[subItemIndex];

    // if they're both empty, return 0
    if (string.IsNullOrEmpty(itemOne.Text) && string.IsNullOrEmpty(itemTwo.Text))
        return 0;

    // if itemOne is empty, it comes second
    if (string.IsNullOrEmpty(itemOne.Text))
        return 1;

    // if itemTwo is empty, it comes second
    if (string.IsNullOrEmpty(itemTwo.Text)
        return -1;

    uint itemOneComparison = uint.Parse(itemOne.Text);
    uint itemTwoComparison = uint.Parse(itemTwo.Text);

    // Calculate correct return value based on object comparison.
    int comparison = itemOneComparison.CompareTo(itemTwoComparison);
    if (OrderOfSort == SortOrder.Descending)
        comparison = (-comparison);

    return comparison;
}

(I might've got the "1" and "-1" for when they're empty back to front, I can never remember :)

Upvotes: 4

MarkMpn
MarkMpn

Reputation: 457

Your // ALWAYS SEND TO BOTTOM/END OF LIST. branch is being executed when either the x or y parameters are empty, i.e. a non-empty value will be sorted according to this rule if it is being compared to an empty value. You probably want something more like this:

if (!string.IsNullOrEmpty(itemOne.Text) && !string.IsNullOrEmpty(itemTwo.Text))
{
    uint itemOneComparison = uint.Parse(itemOne.Text);
    uint itemTwoComparison = uint.Parse(itemTwo.Text);

    comparison = itemOneComparison.CompareTo(itemTwoComparison);
}
else if (!string.IsNullOrEmpty(itemOne.Text)
{
    comparison = -1;
}
else
{
    comparison = 1;
}

Upvotes: 0

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