Check if one IEnumerable contains all elements of another IEnumerable

user_407369 0
Viewed 86070

What is the fastest way to determine if one IEnumerable contains all the elements of another IEnumerable when comparing a field/property of each element in both collections?

public class Item
{
    public string Value;

    public Item(string value)
    {
        Value = value;
    }
}

//example usage

Item[] List1 = {new Item("1"),new Item("a")};
Item[] List2 = {new Item("a"),new Item("b"),new Item("c"),new Item("1")};

bool Contains(IEnumerable<Item> list1, IEnumerable<Item>, list2)
{
    var list1Values = list1.Select(item => item.Value);
    var list2Values = list2.Select(item => item.Value);

    return //are ALL of list1Values in list2Values?
}

Contains(List1,List2) // should return true
Contains(List2,List1) // should return false
ienumerable linq .net c#
8 Answers

You should use HashSet instead of Array.

Example:

List1.SetEquals(List2); //returns true if the collections contains exactly same elements no matter the order they appear in the collection

Reference

The only HasSet limitation is that we can't get item by index like List nor get item by Key like Dictionaries. All you can do is enumerate them(for each, while, etc)

user_56910780

Another way is to convert your superset list to a HashSet and use the IsSuperSet method of HashSet.

bool Contains(IEnumerable<Item> list1, IEnumerable<Item>, list2)
{
    var list1Values = list1.Select(item => item.Value);
    var list2Values = list2.Select(item => item.Value).ToHashSet();

    return list2Values.IsSupersetOf(list1Values);
}
user_16858140
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