Linq Query Dictionary where value in List

Question

I have a Dictionary<string, string> and another List<string>. What I am trying to achieve is a linq query to get all items out of the dictionary where any values from said dictionary are in the List<string>.

I found this post to be helpful, LINQ querying a Dictionary against a List . And was able to write the following linq expression, however my results never actually return anything.

What I have so far.

Data is the dictionary and PersonList is the list of strings.

var Persons = PersonList.Where(x => Data.ContainsKey(x))
                        .Select(z => new { key = z, value = Data[z] })
                        .ToList();

Try replacing PersonList with Data. What you really need is data back from Data dictionary, not PersonList. — Yahya, Feb 11 '14 at 14:21

score 33 · Accepted Answer · answered Feb 11 '14 at 14:24

33

Are you looking for keys or values? If you're looking for values use

var Persons = Data.Where(kvp => PersonList.Contains(kvp.Value))
                  .ToDictionary(kvp => kvp.Key, kvp => kvp.Value);

If instead you really want keys then your code should work but another option would be:

var Persons = Data.Where(kvp => PersonList.Contains(kvp.Key))
                  .ToDictionary(kvp => kvp.Key, kvp => kvp.Value);

answered Feb 11 '14 at 14:24

D Stanley

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This is exactly what I was trying to achieve, and it works flawlessly in my application. Thank you! – mituw16 Feb 11 '14 at 14:30
I tried for hours to get something like that working with the `Select()` method. All I needed was the `ToDictionary()`. Thanks mate! – Sebastian Jan 20 '16 at 08:16
This post helps me to understand how to use `.ToDictionary()` in Linq. Thanks buddy sample code where i used `ToDictionary()` method `ctx.SalesSummaries.ToDictionary(x => x.TableNumber, x => x.Status)` – Niraj Trivedi Aug 09 '17 at 01:37

score 5 · Answer 2 · edited Sep 02 '15 at 13:21

5

Try this one:

var Persons = Data.Where(x=>PersonList.Contains(x.Value))
                  .Select(x=>new { key=x.Key, value=x.Value})
                  .ToList();

I converted the result to a list, because I noticed that you used it in your code. If you want it to a dictionary, just take a look to the answer provided by D Stanley.

edited Sep 02 '15 at 13:21

Michael Eakins

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answered Feb 11 '14 at 14:24

Christos

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score 1 · Answer 3 · answered Feb 11 '14 at 14:42

1

I think you don't have to convert it ToDictionary, because your source is a dictionary:

var Persons = Data.Where(kvp => personList.Contains(kvp.Key))
            .Select(x => x);

I quickly tested it in LinqPad, but if this is a bad idea or I'm wrong, please leave a comment.

answered Feb 11 '14 at 14:42

Rene Hilgers

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This doesn't result in a dictionary, it results in an `IEnumerable>` - the same as an `IEnumerable`, but with the extra overhead of the Key as well. – Zac Faragher Aug 21 '17 at 04:21

Linq Query Dictionary where value in List

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