Getting distinct values from a list of objects with objects

Question

I have a class which has two objects with in it. For example:

public class Animal
{
    public Carnivorous MeatEater { get; set; }
    public Herbivorous VegEater { get; set; }
    public Animal()
    {           
        this.MeatEater = new Carnivorous();
        this.VegEater = new Herbivorous();
    }
}

Carnivorous and Herbivorous have a Category property.

I populated this class with a list of data from my database which is stored in either MeatEater or VegEater. I need to get a distinct list of Category from both and MeatEater and VegEater combined. How can I get this list?

Thanks!

...huh. I kinda thought animals "were" meat eaters or veg eaters, rather than "having" meat eaters or veg eaters. This organization feels difficult to wrap my head around; I'd expect MeatEater to be an interface. — Katana314
– Katana314, Commented Jul 17, 2013 at 15:18
Just to make sure, this list will contain only 0 (no MeatEater or VegEater object present), 1 (either only MeatEater or VegEater has been assigned, or they both have the same category), or 2 distinct categories will be returned here, right? There's no hidden information that "carnivorous" is a list or something? — Lasse V. Karlsen
– Lasse V. Karlsen, Commented Jul 17, 2013 at 15:18
Sorry, If i am not clear. Based on the data validation, i store in meateater or vegeater. for eg. meateater has 2 records: "Trex", a description, "Very Large" (category) & "Lion", a desc, "Medium". veg eater has 2 records: "Cow", a desc, "Medium" and "Lamb", a desc, "Small". I have to get a distinct list with "large", "Medium" and "Small". Hope I am Clear now. — Venkat
– Venkat, Commented Jul 17, 2013 at 15:36

It'sNotALie. · Accepted Answer · 2013-07-17 15:39:05Z

2

If I understood your question correctly, here you go: (this is assuming Category is a string, else you also have to overload Equals in your categories class):

var result = myList.SelectMany(GetValidCategories).Where(s => s != null)
                   .Distinct();

A needed function:

public static IEnumerable<string> GetValidCategories(Animal a)
{
    List<string> categories = new List<string>();
    if (a.MeatEater != null) categories.Add(a.MeatEater.Category);
    if (a.VegEater != null) categories.Add(a.VegEater.Catergory);
    return categories;
}

HOWEVER, this is not a good design. Animals are meat and/or veg eaters. They do not have them.

A better design would be this:

[Flags] public enum AnimalType { Carnivorous = 1, Herbivorous = 2, Ominovorous = 3 }
public class Animal
{
    public AnimalType Type { get; set; }
    public string Category { get; set; }
    //all the other members that Herbivorous + Carnivorous share,
    //so pretty much all of them really.
}

Then, it would be much easier:

var result = myList.Select(a => a.Category).Where(s => s != null).Distinct();

edited Jul 17, 2013 at 15:39

answered Jul 17, 2013 at 15:34

It'sNotALie.

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4 Comments

Moo-Juice Over a year ago

Omnivores would like a word with your assumption. :)

It'sNotALie. Over a year ago

@Moo-Juice [Flags] would like to have a word with yours. :P

Moo-Juice Over a year ago

I meant, your line "Animals are meat or veg eaters"... surely "and/or" is better... as they can be both :)

Moo-Juice Over a year ago

Actually, extending it.. using your Flags solution.. enum AnimalType { Carnivorous = 1, Herbivorous = 2, Ominovorous = 3 }. Problem solved! :)

It'sNotALie. · Accepted Answer · 2013-07-17 15:38:29Z

0

At least one basic approach is to first select them indpendently then union.

using System.Linq;

var query1 = (from animal in myList
    select animal.MeatEater.Category).Distinct();

var query2 = (from animal in myList
    select animal.VegEater.Category).Distinct();

var result = query1.Union(query2);

edited Jul 17, 2013 at 15:38

It'sNotALie.

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answered Jul 17, 2013 at 15:36

Ted

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Comments

Koushik · Accepted Answer · 2013-07-17 15:58:41Z

0

You can add all the categories from meat eaters to a list and all the categories from veg eaters to the same list if the category is not already present.

var lstCategories = new List<string>();

foreach(string category in animal.MeatEater.Category)
    if(!lstCategories.Contains(category))
        lstCategories.add(category);

foreach(string category in animal.VegEater.Category)
    if(!lstCategories.Contains(category))
        lstCategories.add(category);

so finally the lstCategories will have distinct set of combined Categories at the end.

answered Jul 17, 2013 at 15:58

Koushik

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