CODEWITHSUNDEEP
c#linqienumerable
Rire1979
Rire1979

Reputation: 652

Group and concatenate List of tuples

I have a list of pairs (key, val) with both key and value being strings. I want to aggregate the tuples with duplicate keys.

For (key1, val1), (key2, val2), (key3, val3), (key1, val4), (key2, val5)

I want output

(key1, val1+val4), (key2, val2+val5)

This is my current query

var duplicates = Contents.Records.SelectMany(x => x.Users).Select(x => new { Name = x.Name, ID= x.ID}).GroupBy(x => x.ID).Select(x => new { x.Key, Names = x.Select(p=>p.Name).Aggregate((a,b) => a +","+b)}).ToArray();

But at the end for each entry in duplicates the member Names is empty.

The data is as follows each Records has a List Users. Each user has a Name and an ID. What am I doing wrong?

Upvotes: 1

Views: 5622

Answers (1)

Gert Arnold
Gert Arnold

Reputation: 109165

Aggregate looks like it should do the job. But I've never liked Aggregate. The syntax is not intuitive (in my mind). Usually other ways look more lucid. Take this one:

Tuple<string,string>[] tuples = { 
                                    Tuple.Create("key1", "val1"), 
                                    Tuple.Create("key2", "val2"), 
                                    Tuple.Create("key3", "val3"), 
                                    Tuple.Create("key1", "val4"), 
                                    Tuple.Create("key2", "val5")
                                };
tuples.GroupBy(t => t.Item1, t => t.Item2)
      .Select(g => Tuple.Create(g.Key, string.Join("+", g)))
      .Dump(); // Linqpad output command

result:

key1    val1+val4
key2    val2+val5
key3    val3

Upvotes: 1

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