C#•2y ago

✅ How do I merge a list of dictionaries based on keys using LINQ?

So if I have something like: [{ number: 1 }, { number: 2 }, { number: 3 }] I want to get: { number: [1, 2, 3]} I allow duplicates.

11 Replies

Unknown User•2y ago

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TheHelpfulHelperOP•2y ago

using LINQ

Unknown User•2y ago

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mtreit•2y ago

Mixing numbers and letters in one dictionary seems odd; what are the TKey and TValue types for your dictionaries? Just string?

TheHelpfulHelperOP•2y ago

Yeah I just realized that as well, my example wasnt well constructed. I am essentially trying to get the fields of a type using reflection and they all have a type that implements the same interface. So the type of the dictionary is Dictionary<string, IInterface> And I need to get the values of multiple of objects of the same type in a single dictionary based on the field name So the output type is Dictionary<string, List<IInterface>>

Unknown User•2y ago

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TheHelpfulHelperOP•2y ago

Alright I fiddled around and came up with this:

dictionaries
  .SelectMany(dict => dict)
  .ToLookup(pair => pair.Key, pair => pair.Value)
  .ToDictionary(grouping => grouping.Key, grouping => grouping.ToList());

dictionaries
  .SelectMany(dict => dict)
  .ToLookup(pair => pair.Key, pair => pair.Value)
  .ToDictionary(grouping => grouping.Key, grouping => grouping.ToList());

This actually does what I want.

Unknown User•2y ago

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mtreit•2y ago

The benchmark results do not favor LINQ here FYI 🙂

mtreit•2y ago

(Of course, when do the benchmark results ever favor LINQ?)

TheHelpfulHelperOP•2y ago

its manually triggered by UI interaction, so performance is not a concern

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✅ How do I merge a list of dictionaries based on keys using LINQ?