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

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();
    }
}