Select Items from List using Array

Question

Is there a better way to write this procedure?

    public List<IDenomination> GetInventory(int[] denominations)
    {
        var inventory = new List<IDenomination>();

        foreach (var denomination in denominations)
        {
            foreach (var item in Account)
            {
                if (item.Currency == denomination)
                {
                    inventory.Add(item);
                }
            }
        }

        return inventory;
    }

Answer 1

You could use some linq to do this fairly easily. Converting the array to a HashSet will allow Contains to operate faster

public List<IDenomination> GetInventory(int[] denominations)
{
    var denoms = new HashSet<int>(denominations);
    return Account.Where( a => denoms.Contains(a.Currency) ).ToList();
}

This assumes that Account : IDenomination though, as does your original code. If that were not the case, you would use a .Select() prior to .ToList() in order to select the IDenomination from Account.

Answer 2

It's really not a great idea to return a List from your method if you can help it. You've effectively bound your code to always using a list. What if your client wants to use a FancyCustomList<IDenomination>? You'd have to do some messy casting.

By all means, use the Linq that @TravisJ provider, but you should change the signature to return a IList<IDenomination> instead.