Filter Linq EXCEPT on properties

Try a simple where query

var filtered = unfilteredApps.Where(i => !excludedAppIds.Contains(i.Id));

The except method uses equality, your lists contain objects of different types, so none of the items they contain will be equal!

ColinE's answer is simple and elegant. If your lists are larger and provided that the excluded apps list is sorted, BinarySearch<T> may prove faster than Contains.

EXAMPLE:

unfilteredApps.Where(i => excludedAppIds.BinarySearch(i.Id) < 0);

I use an extension method for Except, that allows you to compare Apples with Oranges as long as they both have something common that can be used to compare them, like an Id or Key.

public static class ExtensionMethods
{
    public static IEnumerable<TA> Except<TA, TB, TK>(
        this IEnumerable<TA> a,
        IEnumerable<TB> b,
        Func<TA, TK> selectKeyA,
        Func<TB, TK> selectKeyB, 
        IEqualityComparer<TK> comparer = null)
    {
        return a.Where(aItem => !b.Select(bItem => selectKeyB(bItem)).Contains(selectKeyA(aItem), comparer));
    }
}

then use it something like this:

var filteredApps = unfilteredApps.Except(excludedAppIds, a => a.Id, b => b);

the extension is very similar to ColinE 's answer, it's just packaged up into a neat extension that can be reused without to much mental overhead.

Filter Linq EXCEPT on properties

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