score:3

Accepted answer

Well, you can certainly express it in LINQ easily:

var x = from value in values
        group value by ranges.Where(x => value >= x)
                             .DefaultIfEmpty()
                             .Last();

But I very much doubt that that will work in LINQ to SQL. Basically you've got to find a simple way of mapping a value to one of those categories.

Complete example:

using System;
using System.Linq;
using System.Collections.Generic;

class Test
{
    static void Main()
    {
        int[] values = {100, 110, 120, 130, 140, 150, 160, 170};
        int[] ranges = {115, 145, 180};

        var query = from value in values
                    group value by ranges.Where(x => value >= x)
                                         .DefaultIfEmpty()
                                         .Last();

        foreach (var group in query)
        {
            Console.WriteLine("{0}: {{{1}}}", group.Key, 
                              string.Join(", ", group));
        }
    }
}

Output:

0: {100, 110}
115: {120, 130, 140}
145: {150, 160, 170}

Note that this won't include any categories which don't have any values in.

Also note that this would be simpler (using First() instead of Last()) if you'd be happy to categorize slightly differently:

115: {100, 110}
145: {120, 130, 140}
180: {150, 160, 170}

In other words, if the category was defined by the first range value higher than the row value.

EDIT: Here's a version which gives the empty groups. It's pretty horrible though, IMO:

var query = from range in ranges
            join value in values
            on range equals ranges.Where(x => value >= x)
                                  .DefaultIfEmpty()
                                  .Last() into groups
            select new { Key = range, Values = groups};

foreach (var group in query)
{
    Console.WriteLine("{0}: {{{1}}}", group.Key, 
                      string.Join(", ", group.Values));
}

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