LINQ C# - Combining multiple groups

Question

LINQ Groupby query creates a new group for each unique key. I would like to combine multiple groups into a single group based on the key value.

e.g.

var customersData = new[] 
{
    new { id = 1, company = "ABC" },
    new { id = 2, company = "AAA" },
    new { id = 3, company = "ABCD" },
    new { id = 4, company = "XYZ" },
    new { id = 5, company = "X.Y.Z." },
    new { id = 6, company = "QQQ" },
};

var groups = from d in customersData 
             group d by d.company;

Let's say I want ABC, AAA, and ABCD in the same group, and XYZ, X.Y.Z. in the same group.

Is there anyway to achieve this through LINQ queries?

Answer 1

I am assuming the following:

1. You meant to have quotes surrounding the company "names" (as below).
2. Your problem is simply solved by removing the '.'s from each company name.

If these assumptions are correct, the solution is simply the following:

var customersData = new[] {
    new { id = 1, company = "ABC" },
    new { id = 2, company = "A.B.C." },
    new { id = 3, company = "A.B.C." },
    new { id = 4, company = "XYZ" },
    new { id = 5, company = "X.Y.Z." },
    new { id = 6, company = "QQQ" },
};

var groups = from d in customersData
             group d by d.company.Replace(".", "");

If these assumptions are not correct, please clarify and I can help work closer to a solution.

Answer 2

var groups = from d in customersData 
             group d by d.company.Replace(".", "");

Answer 3

You will need to use the overload of GroupBy that takes an IEqualityComparer.

var groups = customersData.GroupBy(k => k.company, new KeyComparer());

where KeyComparer could look like

public class KeyComparer : IEqualityComparer
{
    public bool Equals(string x, string y)
    {
        // put your comparison logic here 
    }

    public int GetHashCode(string obj)
    {
        // same comparison logic here
    }
}

You can comparer the strings any way you like in the Equals method of KeyComparer.

EDIT:

You also need to make sure that the implementation of GetHashCode obeys the same rules as the Equals method. For example if you just removed the "." and replaced with "" as in other answers you need to do it in both methods like this

public class KeyComparer : IEqualityComparer
{
    public bool Equals(string x, string y)
    {
        return x.Replace(".", "") == y.Replace(".", "");
    }

    public int GetHashCode(string obj)
    {
        return obj.Replace(".", "").GetHashCode();
    }
}

Answer 4

public void int GetId(Company c)
{
  int result = //whatever you want
  return result;
}

then later:

var groups = from d in customersData
             group d by GetId(d.company);

Answer 5

I think this is what you want:

        var customersData = new[]  
        { 
            new { id = 1, company = "ABC" }, 
            new { id = 2, company = "AAA" }, 
            new { id = 3, company = "ABCD" }, 
            new { id = 4, company = "XYZ" }, 
            new { id = 5, company = "X.Y.Z." }, 
            new { id = 6, company = "QQQ" }, 
        };

        var groups = from d in customersData
                     group d by d.company[0];

        foreach (var group in groups)
        {
            Console.WriteLine("Group " + group.Key);
            foreach (var item in group)
            {
                Console.WriteLine("Item " + item.company);
            }
        }
        Console.ReadLine();