Question

LINQ to objects is my best friend. I am using often the ConvertAll extension method to achieve a conversion.

However I realize I can achieve the same by using the Select extension method.

For example, I have a ListView that displays a list of Alarm objects. I store the object itself in the Tag property of a ListView element. Then I retrieve the selection this way :

Version with ConvertAll:

public Alarm[] SelectedTags
{
    get
    {
        return AlarmListView
               .SelectedItems
               .OfType<ListViewItem>()
               .ToList().ConvertAll(i => i.Tag as Alarm)
               .ToArray();
    }
}

Version with Select:

public Alarm[] SelectedTags
{
    get
    {
        return AlarmListView
               .SelectedItems
               .OfType<ListViewItem>()
               .Select(i => i.Tag as Alarm)
               .ToArray();
    }
}

Personally I prefer Select because I can convert my collections easily without having to put them in a List and use ConvertAll. Anyway, both have certainly good reasons to exists.

Is one better than the other ? In which scenarios ?

Answer 1

ConvertAll has been around since .Net 2.0, whereas LINQ is newer. Select appears to be more general, and to make ConvertAll redundant.

I can’t think of any situation where you would need to use ConvertAll in new code. Select is better-known, more general, and works with the other features of LINQ (such as direct translation to SQL queries in LINQ to SQL).