Sorting using C#'s Linq library

Question

I am creating a C# 2010 application using .NET Framework 3.5.

I have a datagridview that contains a few columns and rows [obviously]. I save this datagridview's rows in a structure of the form List<string[]>. I also have a List<double> which contains coefficients. I want to sort the structure by the coefficients using the System.LINQ library. I have attempted the following:

var linq_Query_rowrates =
    from rw in rows
    orderby matchrate descending
    select rw;

This underlines the rows in the query and shows the following error:

Error 1 Could not find an implementation of the query pattern for source type 'System.Collections.Generic.List<string[]>'. 'OrderByDescending' not found. Are you missing a reference to 'System.Core.dll' or a using directive for 'System.Linq'?

Is it possible to sort this kind of structure using the LINQ library and if yes, how?

Note: I am aware of a lot of other methods to accomplish this, I am just interested in doing it using the LINQ library.

Note: matchrate is not a member of rows but using a member of rows does not work either.

LATER EDIT: Maybe it should be something like this?

        var linq_Query_rowrates =
            from rw in rows
            join rate in matchrate
            on matchrate equals rows
            orderby matchrate descending
            select rw;

Have you referenced 'System.Core.dll' and included a using System.Linq; directive in your source file? — dtb
– dtb, Commented May 30, 2012 at 13:07
@dtb, yes, I have included using System.Linq; and have referenced the dll. — Vlad Schnakovszki
– Vlad Schnakovszki, Commented May 30, 2012 at 13:10

jrummell · Accepted Answer · 2012-05-30 14:06:36Z

3

Assuming matchrate is a member of rw, you need to use the following syntax:

var linq_Query_rowrates =
    from rw in rows
    orderby rw.matchrate descending
    select rw;

Update

Ideally, you would have a navigation property for your rate relationship, so your query would look like this:

var linq_Query_rowrates =
    from rw in rows
    orderby rw.rate.matchrate descending
    select rw;

Another option is to perform a join. But joins in LINQ are ugly, and I try to avoid them.

edited May 30, 2012 at 14:06

answered May 30, 2012 at 13:07

jrummell

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7 Comments

Vlad Schnakovszki Over a year ago

It is not a member but using a member of rows doesn't work either.

jrummell Over a year ago

You can't order by something that isn't a member of rw's type.

Vlad Schnakovszki Over a year ago

Ok, is there any way to sort rows by matchrate using only LINQ?

Vlad Schnakovszki Over a year ago

Perhaps something like this might work? var linq_Query_rowrates = from rw in rows join rate in matchrate on matchrate equals rows orderby matchrate descending select rw;

jrummell Over a year ago

Yes, you can do this with a join.

|

clearpath · Accepted Answer · 2012-05-30 13:36:19Z

2

It's ugly, but it's Linq:

            List<string[]> rows = null;
            List<double> coefficients = null;

            rows
                .Select((row, index) => new { Row = row, Index = index })
                .Join(coefficients
                            .Select(
                                (coefficient, index) => new { Coefficient = coefficient, Index = index }), 
                                x => x.Index, 
                                x => x.Index, 
                                (rowIndex, coefIndex) => new { Row = rowIndex.Row, Coefficient = coefIndex.Coefficient })
                .OrderBy(x => x.Coefficient)
                .Select(x => x.Row);

I haven't tested it though. It should be possible to transform it to query form.

answered May 30, 2012 at 13:36

clearpath

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2 Comments

Vlad Schnakovszki Over a year ago

I need it to sort descending actually. How would I go about doing this?

jrummell Over a year ago

Replace OrderBy with OrderByDescending.

Jason Larke · Accepted Answer · 2012-05-30 14:02:52Z

If your collection of coefficients are meant to link with your collection of string[], why do you build 2 seperate, unrelated lists? Surely it would be more robust to just build a very simple structure to hold all the information to ensure there are always appropriate coefficients for each row. It also makes sorting very straightforward.

public struct CoefficientRow
{
    public double Coefficient;
    public string[] Cells;

    public CoefficientRow(double c, string[] cells)
    {
        this.Coefficient = c;
        this.Cells = cells;
    }
}

Sorting becomes a breeze...

List<CoefficientRow> rows = new List<CoefficientRow>();
//populate the list...
var orderedRows = rows.OrderBy(cr => cr.Coefficient);
//or
var orderedRows = rows.OrderByDescending(cr => cr.Coefficient);

Inserting them to the datagridview is also still quite easy:

foreach(var row in rows)
    this.dgvDataView.Rows.Add(row.Cells);

Amy B · Accepted Answer · 2012-05-31 20:51:21Z

1

If you could use .Net4, user676571's answer simplifies to:

IEnumerable<string> query = rows
  .Zip(coefficients, (r, c) => new {row = r, coef = c})
  .OrderByDescending(x => x.coef)
  .Select(x => x.row);

answered May 31, 2012 at 20:51

Amy B

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