LINQ datarow string to array and then into to string list

Question

I have some code that will loop over DataRows and will split a pipe delimited column in the DataRow into an array, and then into a List<string>.

Is there a better way to do this using LINQ? I've tried but got nowhere!

List<string> allSizes = new List<string>();

foreach (DataRow resultRow in results.Rows)
{
    if (resultRow["Sizes"] != DBNull.Value)
    {
        string[] sizes = resultRow["Sizes"].ToString().Split('|');
        foreach (string size in sizes)
        {
            if (!allSizes.Contains(size))
            {
                allSizes.Add(size);
            }
        }
    }
}

Note that using Contains on a List isn't particularly efficient. Considering that it's likely that the data set could get large, and you check whether it's in the list or not for each item, that could get expensive. It's better to use a set-based data structure to perform a Distinct, which is what you're doing, and what the LINQ Distinct method does. — Servy
– Servy, Commented Oct 22, 2012 at 19:08

Servy · Accepted Answer · 2012-10-22 19:05:36Z

10

var allSizes = results.Rows.Cast<DataRow>()
    .Where(row => row["Sizes"] != DBNull.Value)
    .SelectMany(row => row["Sizes"].ToString().Split('|'))
    .Distinct()
    .ToList();

answered Oct 22, 2012 at 19:05

Servy

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1 Comment

Laurence Over a year ago

Extension methods look much better :) +1

Laurence · Accepted Answer · 2012-10-22 19:08:17Z

0

Here is the LINQ version but personally I don't find it much cleaner:

var allSizes = new List<string>();

foreach (
    string size in 
    from DataRow resultRow in results.Rows 
    where resultRow["Sizes"] != DBNull.Value 
    select resultRow["Sizes"].ToString().Split('|') into sizes 
    from size in sizes where !allSizes.Contains(size) 
    select size) {
    allSizes.Add(size);
}

answered Oct 22, 2012 at 19:08

Laurence

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1 Comment

Servy Over a year ago

As noted to OP, performing a contains on a List of nontrivial size isn't a cheap operation; you should be putting the items into a set-based data structure to perform the distinct.

Gebb · Accepted Answer · 2012-10-22 19:14:24Z

0

Something like this.

var linqSizes =
    from row in results.Rows
    where row["Sizes"] != DBNull.Value
    let sizes = row["Sizes"].ToString().Split('|')
    from size in sizes
    group size by size into g
    select g.Key;

The variable linqSizes will contain the same elements as your variable allSizes.

answered Oct 22, 2012 at 19:14

Gebb

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Comments

code4life · Accepted Answer · 2012-10-22 19:14:37Z

0

Strong-typed DataRow and LINQ:

dt.Rows.OfType<DataRow>().Where(r => r["Sizes"] != DBNull.Value)
      .SelectMany(r=>r.Field<string>("Sizes").Split('|')
      .Distinct().ToList();

answered Oct 22, 2012 at 19:14

code4life

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