Question

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.

Answer 1

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 🙂