How can I use LINQ to "prune" a dictionary?

Question

I have a Dictionary and a List of keys to remove from the dictionary. This is my implementation right now:

var keys = (from entry in etimes
            where Convert.ToInt64(entry.Value) < Convert.ToInt64(stime)
            select entry.Key).ToList();

foreach (var key in keys)
{
    etimes.Remove(key);
    count--;
}

Is there something I can do the eliminate the foreach loop?

Answer 1

var pruned = etimes.Where(entry => Convert.ToInt64(entry.Value) >= 
    Convert.ToInt64(stime)).ToDictionary(entry => entry.Key, 
        entry => entry.Value);

This statement simply filters the dictionary using the LINQ Where function to select which items to keep rather than those to remove (which then requires further code, as you showed). The ToDictionary converts thwe IEnumerable<KeyValuePair<TKey, TValue>> to the desire Dictionary<TKey, TValue> type, and is at least quite simple, if not terribly elegant or efficient due to the need to specify the two lambda expressions to select the key and value from a KeyValuePair (and then creating a new dictionary). Saying this, I don't really see it as a problem, especially if the dictionary is small and/or number of items being removed is large.

Answer 2

Well, performance or readability issues aside, couldn't this also be done something like the following:

<Extension> void itemDelete(List l, object item) {
    l.Remove(item)
}

var keys = (from entry in etimes
        where Convert.ToInt64(entry.Value) < Convert.ToInt64(stime)
        select entry.Key).ToList();

keys.foreach(itemDelete());

Forgive my coding, I'm not 100% certain of the exact syntax (especially in C#); consider that pseudo-code. Note the addition of the new function, and the .foreach function on the end of the LINQ query. I know this would be possible in VB, i assume C# has something similar... if not you could always write your own .foreach extension. It may or may not improve anything, but it's an idea.