Can LINQ do this for me?

Question

Hi.. new with Linq and very excited with this feature. However, I want to see if I can do the following with LINQ:

DataView source = (DataView) MyDataGrid.ItemsSource;

foreach (DataRowView vw in source)
 {
      if (vw.Row[dummyColumnIndex] != null && 
         vw.Row[dummyColumnIndex].ToString() == DisplayValue)
      {
            vw.Row[dummyColumnIndex] = string.Empty;
            break;
      }
 }

Notice that I have a break in my foreach loop, meaning that I just need to reset the first match row's column value to empty string.

Thanks!

Answer 1

var firstMatch = source
    .Cast<DataRowView>()
    .First(vw => vw.Row[dummyColumnIndex] != null && vw.Row[dummyColumnIndex].ToString() == DisplayValue);
firstMatch.Row[dummyColumnIndex] = string.Empty;

Note that this will throw an exception if there's no match, so you could also do:

var firstMatch = source
    .Cast<DataRowView>()
    .FirstOrDefault(vw => vw.Row[dummyColumnIndex] != null && vw.Row[dummyColumnIndex].ToString() == DisplayValue);

if(firstMatch != null)
    firstMatch.Row[dummyColumnIndex] = string.Empty;

Answer 2

Yes it can. I tend to prefer the query syntax:

    var query = from vw in source.Cast<DataRowView>()
                where vw.Row[dummyColumnIndex] != null &&
                vw.Row[dummyColumnIndex].ToString() == DisplayValue
                select vw;

    var item = query.FirstOrDefault();
    if (item != null)
       item.Row[dummyColumnIndex] = "";

As noted by others: its best to use 'FirstOrDefault' to avoid throwing an exception if you don't find a match.

Answer 3

Yes, but you'll need to use the Cast method of IEnumerable to cast this over to a generic IEnumerable where the Type argument is 'DataRowView', then you can do something like this. This will use the provided logic (in the form of a lambda expression) to evaluate each record in the DataView to determine if it's a match. It'll return the first one it finds, or 'null' if none are found. You can handle the null anyway you want; I usually like to throw exceptions in case like that unless there's a valid reason that no match might be found.

        var match = source.Cast<DataRowView>().FirstOrDefault(
                        s => s[dummyColumnIndex] != null && 
                            s[dummyColumnIndex].ToString() == DisplayValue);

        if (match == null)
          throw new Exception("Could not find match for " + DisplayValue);

        match[dummyColumnIndex] = String.Empty;

Answer 4

If the Objective is to find something in a list
{
if (sorted) http://en.wikipedia.org/wiki/Search%5Falgorithms
else if(efficent) http://en.wikipedia.org/wiki/Sort%5Falgorithms
else i don`t know
}