how to remove objects from list by multiple variables using linq

Question

I want to remove objects from a list using linq, for example :

public class Item
{
    public string number;
    public string supplier;
    public string place;
}

Now i want to remove all of the items with the same number and supplier that appear more then once.
Thanks

I assume appear in the least more then one should read appear in the list more than once — fearofawhackplanet
– fearofawhackplanet, Commented Jul 19, 2011 at 14:26

Ani · Accepted Answer · 2011-07-19 14:38:55Z

5

This would be slightly tedious to do in-place, but if you don't mind creating a new list, you can use LINQ.

The easiest way to specify your definition of item-equality is to project to an instance of an anonymous-type - the C# compiler adds a sensible equality-implementation on your behalf:

List<Item> items = ...

// If you mean remove any of the 'duplicates' arbitrarily. 
List<Item> filteredItems = items.GroupBy(item => new { item.number, item.supplier })
                                .Select(group => group.First())
                                .ToList();

// If you mean remove -all- of the items that have at least one 'duplicate'.
List<Item> filteredItems = items.GroupBy(item => new { item.number, item.supplier })
                                .Where(group => group.Count() == 1)
                                .Select(group => group.Single())
                                .ToList();

If my first guess was correct, you can also consider writing an IEqualityComparer<Item> and then using the Distinct operator:

IEqualityComparer<Item> equalityComparer = new NumberAndSupplierComparer();
List<Item> filteredItems = items.Distinct(equalityComparer).ToList();

Btw, it's not conventional for types to expose public fields (use properties) or for public members to have camel-case names (use pascal-case). This would be more idiomatic:

public class Item
{
    public string Number { get; set; }
    public string Supplier { get; set; }
    public string Place { get; set; }
}

edited Jul 19, 2011 at 14:38

answered Jul 19, 2011 at 14:24

Ani

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4 Comments

guyl Over a year ago

i will try that, nice job for the quick thinking.

guyl Over a year ago

Is it possible to use it without the new { item.NUmber , item.Supplier} and keep the original class ?

guyl Over a year ago

Let me just say that what is very hard on the one hand could be a lot easier on the other, meaning (that i am an idiot) let pick the items with more then 1 rather remove the items that are distinct. now how can i group them by more then on property ?

Ani Over a year ago

To group them by more than one property, the easiest way is to use the anonymous-type projection like I've mentioned. To pick the ones that have at least 1 dupe, try: items.GroupBy(--).Where(group => group.Count() > 1).SelectMany(group => group).ToList()

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