CODEWITHSUNDEEP
c#linqdictionary
boywonder
boywonder

Reputation: 116

Invert and flatten a dictionary using LINQ

I have something that looks like:

{
  "Item1": ["1a", "1b", "1c"],
  "Item2": ["2a"],
  "Item3": ["3a", "3b"]
}

What I want is this:

{
  
  "1a": "Item1", 
  "1b": "Item1", 
  "1c": "Item1",
  "2a": "Item2",
  "3a": "Item3", 
  "3b": "Item3"
}

I've been able to do this, but just wondering if there is a more concise LINQ way?

Dictionary<string, string[]> items = new Dictionary<string, string[]>(...);
Dictionary<string, string> endResult = new Dictionary<string, string>(); // This is correct

var reversed = items.ToDictionary(x => x.Value, x => x.Key);

foreach (var item in reversed)
{
    foreach (var inner in item.Key)
    {
        endResult.Add(inner, item.Value);
    }
}

Upvotes: 0

Views: 205

Answers (2)

canton7
canton7

Reputation: 42225

To add a slightly more concise way, taking advantage of the fact that Dictionary<TKey, TValue> has a constructor which accepts an IEnumerable<KeyValuePair<TKey, TValue>>:

Dictionary<string, string> result = new(
    input.SelectMany(kvp => kvp.Value.Select(v => KeyValuePair.Create(v, kvp.Key))));

Upvotes: 1

Backs
Backs

Reputation: 24903

Dictionary<string, string> endResult = items.Select(o => o.Value.Select(v => new { Value = v, Key = o.Key }))
                                            .SelectMany(o => o)
                                            .ToDictionary(o => o.Value, o => o.Key);

Upvotes: 2

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