Linq group the columns combination to a two list

Question

I have question about how I could use Linq grouping the same combination that the list has then relate to a two list.

Example:

I have theses classes.

public class PetCategoryOwner
{
    public string PetCategory { get; set; }
    public string Owner { get; set; }
}

public class PetCategoriesOwners
{
    public IEnumerable<string> PetCategories { get; set; }
    public IEnumerable<string> Owners { get; set; }
}

The example data.

Owner	Pet Category
Higa	Terry
Higa	Charlotte
Oliver	Terry
Oliver	Charlotte
Oliver	Chausie
Price	Chausie
Liam	Terry
Liam	Chartreux

var petCategoryOwner = new List<PetCategoryOwner>()
{
    new PetCategoryOwner { Owner = "Higa", PetCategory = "Terry"},
    new PetCategoryOwner { Owner = "Higa", PetCategory = "Charlotte"},
    new PetCategoryOwner { Owner = "Oliver", PetCategory = "Terry"},
    new PetCategoryOwner { Owner = "Oliver", PetCategory = "Charlotte"},
    new PetCategoryOwner { Owner = "Oliver", PetCategory = "Chausie"},
    new PetCategoryOwner { Owner = "Price", PetCategory = "Chausie"},
    new PetCategoryOwner { Owner = "Liam", PetCategory = "Terry"},
    new PetCategoryOwner { Owner = "Liam", PetCategory = "Chartreux"}
};

Expected values

Owner	Pet Category	Group
Higa	Terry	A
Higa	Charlotte	A
Oliver	Terry	A
Oliver	Charlotte	A
Oliver	Chausie	B
Price	Chausie	B
Liam	Terry	C
Liam	Chartreux	C

var petCategoriesOwners = new List<PetCategoriesOwners>()
{
    new PetCategoriesOwners()
    {
        PetCategories = new List<string>() { "Terry", "Charlotte" },
        Owners = new List<string>() { "Oliver", "Higa" }
    },
    new PetCategoriesOwners()
    {
        PetCategories = new List<string>() { "Chausie" },
        Owners = new List<string>() { "Oliver", "Price" }
    },
    new PetCategoriesOwners()
    {
        PetCategories = new List<string>() { "Chartreux", "Terry" },
        Owners = new List<string>() { "Liam" }
    }
}

Answer 1

In order to solve your problem you need to do two steps: group by owners and merge owners based on the fact other group's set is a subset of current owner. You can try to achieve it by running below LINQ query:

public class PetCategoriesOwners
{
    public List<string> PetCategories { get; set; }
    public List<string> Owners { get; set; }
}

var petCategoriesOwners = petCategoryOwner
    .GroupBy(x => x.Owner)
    .Select(x => new
    {
        Owner = x.Key,
        Categories = x.Select(y => y.PetCategory)
    })
    .OrderBy(x => x.Categories.Count())
    .Aggregate(new List<PetCategoriesOwners>(), (acc, current) =>
    {
        var currentCategories = current.Categories.ToList();
        var matches = acc.Where(group => group.PetCategories.All(x => currentCategories.Contains(x)));

        foreach(var match in matches)
        {
            match.Owners.Add(current.Owner);
            currentCategories = currentCategories.Except(match.PetCategories).ToList();
        }

        if (currentCategories.Any())
        {
            acc.Add(
                new PetCategoriesOwners() { 
                    Owners = new List<string>() { current.Owner }, 
                    PetCategories = currentCategories 
                });
        }

        return acc;
    });

So it's important to group by Owner, process groups in ascending order in terms of length. The Aggregate method basically tries to find if previosly entered item overlaps with currently processed one. If it happens then we take those intersecting elements, add owner there and remove those from current element. If any element is left then we create own group for such owner.

Edit: .NET Fiddle