Dictionary has duplicate keys in c# with toDictionary

Question

I'm trying to eliminate the duplicate strings from the list with the list.District() and the toDictionary but it doesn't work.

Any recommendation how I can eliminate the duplication code with Linq?

here is my code

    [JsonIgnore]
    public Dictionary<string, int> SensorValues => InOrderSensorValues
      .ToDictionary(
         x => x.Split(':')[0].ToUpper(), 
         x => int.Parse(x.Split(':')[1]));

And then i want to split the words as above

What do you mean by "it doesn't work"? What is `InOrderSensorValues`? What did you expect `SensorValues` to be? What is it actually? — Sweeper, Nov 12 '19 at 13:27
Please provide a [mre] of the problem you are seeing. That should include a small sample of the data in `InOrderSensorValues` that produces the the duplicates. — Heretic Monkey, Nov 12 '19 at 13:31
@Sweeper, SensorValues is a simple list with a string value, such as "Sensor1:2" and I'm trying to split the string. I want to put the Sendor1 as a key into the dictionary and value of 2 etc — Csibi Norbert, Nov 12 '19 at 13:35
@CsibiNorbert Can't you just do `Distinct` before `ToDictionary`? — Sweeper, Nov 12 '19 at 13:40
@Sweeper That wouldn't help - the duplicate keys come from the `Split`, and a `Distinct` is against the whole object. An extension method `DistinctBy` is what would be used, or `ToLookup` then `ToDictionary`. — NetMage, Nov 12 '19 at 22:08

Tanveer Badar · Accepted Answer · 2019-11-12T13:53:18.890

3

ToDictionary() fails on duplicate keys by design. You can either filter out your data, or insert a GroupBy() before it to eliminate duplicate entries.

Lastly, you can also consider ToLookup() which does tolerate duplicate keys.

Adding GroupBy() would be like this:

public Dictionary<string, int> SensorValues => 
     InOrderSensorValues.GroupBy(x => x.Split(':')[0].ToUpper()).
     ToDictionary(g => g.Key, g => int.Parse(g.First().Split(':')[1]));

edited Nov 12 '19 at 13:53

answered Nov 12 '19 at 13:27

Tanveer Badar

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It says g does not exist in the context. When i say g.First() – Csibi Norbert Nov 12 '19 at 13:49

score 2 · Answer 2 · answered Nov 12 '19 at 22:51

You can use Select to save the Split string and then GroupBy the key, then create a Dictionary using a selection method for the multiple values - I chose First:

public Dictionary<string, int> SensorValues => InOrderSensorValues
      .Select(sv => sv.Split(':'))
      .GroupBy(svp => svp[0].ToUpper(), svp => svp[1])
      .ToDictionary(
         kvp => kvp.Key, 
         kvp => int.Parse(kvp.First()));

Dictionary has duplicate keys in c# with toDictionary

2 Answers2