ConcurrentDictionary AddOrUpdate a list

Question

I'm trying to use a ConcurrentDictionary to help with a filtering task.

If a number appears in list, then I want to copy an entry from one dictionary to another.

But this part of the AddOrUpdate is not right - v.Add(number)

I get

"Cannot implicitly convert type 'void' to 'System.Collections.Generic.List'

And two more errors.

class Program
{
    static void Main(string[] args)
    {
        Program p = new Program();
        List<int> filter = new List<int> {1,2};
        p.Filter(filter);
    }


    private void Filter(List<int> filter)
    {
        Dictionary<string, List<int>> unfilteredResults = new Dictionary<string, List<int>>();
        unfilteredResults.Add("key1", new List<int> { 1,2,3,4,5});

        ConcurrentDictionary<string, List<int>> filteredResults = new ConcurrentDictionary<string, List<int>>();

        foreach (KeyValuePair<string, List<int>> unfilteredResult in unfilteredResults)
        {
            foreach (int number in unfilteredResult.Value)
            {
                if (filter.Contains(number))
                {
                    filteredResults.AddOrUpdate(unfilteredResult.Key, new List<int> { number }, (k, v) => v.Add(number));
                }
            }
        }
    }
}

What are you trying to do? What is the `Filter` expected to do? — Yacoub Massad, Feb 02 '16 at 23:32
@LucasTrzesniewski please make that an answer and I will accept :) thanks for you help — Bryan, Feb 02 '16 at 23:38
@YacoubMassad I'm trying to fund out how to use AddOrUpdate with a list as the value in a concurrent dictionary. The example given bears little relation to my real intention. Lucas has solved it for me. — Bryan, Feb 02 '16 at 23:39
It's a simple API misuse, I don't think I can't get a good enough answer out of this ;) — Lucas Trzesniewski, Feb 02 '16 at 23:42
ok. I'll add an answer shortly so that others can see it easily. Thanks again — Bryan, Feb 02 '16 at 23:57

score 6 · Accepted Answer · answered Mar 11 '16 at 19:05

6

Thanks to Lucas Trzesniewski, for pointing out my mistake in the comments - he didn't want to post an answer.

You probably mean: (k, v) => { v.Add(number); return v; }

answered Mar 11 '16 at 19:05

Bryan

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ConcurrentDictionary AddOrUpdate a list

1 Answers1