C# - Convert delimited string array w/ duplicates to dictionary using LINQ

Question

Given

string[] array = new string[]
{
   "Sample1:foo",
   "Sample2:bar",
   "Sample1:foo1"
}

I know I can convert it to a dictionary this way:

Dictionary<string, string> whatever = new Dictionary<string, string>
foreach (string s in array) do...
  string sampleNumber = s.Substring(0, indexOfColon);
  string fooOrBar= s.Substring(indexOfColon + 1);
  whatever[sampleNumber] = fooOrBar;

And this will prevent an aggregate exception being thrown when a duplicate key is added (although overriding the key, which is fine in this case). Can I do this with LINQ? I am trying something along the lines of:

Dictionary<string, string> whatever = array.ToDictionary(
 key => key.Split(':')[0], value => value.Split(':')[1]);

Is there a way to do this without creating a lookup beforehand?

In the case you want to keep the duplicates, you can use List<Tuple<string, string>> with a one-liner List<Tuple<string, string>> whatever = array.Select(key => new Tuple<string, string>(key.Split(':')[0], key.Split(':')[1])).ToList(); — Keyur PATEL
– Keyur PATEL, Commented Sep 19, 2017 at 3:00

Enigmativity · Accepted Answer · 2017-09-19 02:52:43Z

4

Try this:

Dictionary<string, string> whatever =
    array
        .Reverse()
        .GroupBy(key => key.Split(':')[0])
        .SelectMany(x => x.Take(1))
        .ToDictionary(key => key.Split(':')[0], value => value.Split(':')[1]);

It gives:

Or you could do this:

Dictionary<string, string> whatever =
    array
        .Aggregate(
            new Dictionary<string, string>(),
            (d, v) => { d[v.Split(':')[0]] = v.Split(':')[1]; return d; });

Same result.

answered Sep 19, 2017 at 2:52

Enigmativity

117k12 gold badges101 silver badges184 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

dev way Over a year ago

Worked perfect.

Keyur PATEL Over a year ago

Great idea! An alternative, possibly shorter method than using reverse and select many, is to just use Last(), not sure about the time difference, but var whatever = array.GroupBy(p => p.Split(':')[0]).ToDictionary(key => key.Key, value => value.Last().Split(':')[1]);.

Enigmativity Over a year ago

@KeyurPATEL - I like your approach, but I do try to choose options that avoid .Last() or .First(). I know it doesn't matter with a .GroupBy(...) but I like keeping a good habit.

Cheng Chen · Accepted Answer · 2017-09-19 02:58:01Z

2

What you want is definitely not a Dictionary<string, string> because keys are duplicated. It can be a Dictionary<string, List<string>>, but IMO it's much more like a a ILookup<string, string>:

var result = array
            .Select(a =>
            {
                var parts = a.Split(':');
                return new
                {
                    Key = parts[0],
                    Value = parts[1]   //maybe you need to check something here
                };
            })
            .ToLookup(o => o.Key, o => o.Value);

answered Sep 19, 2017 at 2:58

Cheng Chen

43.7k18 gold badges118 silver badges184 bronze badges

Comments

wittpeng · Accepted Answer · 2017-09-19 03:13:58Z

1

I am not sure how you deal with the value , maybe you can try this:

var list = array.Select(m => new { Key = m.Split(':')[0], Value = m.Split(':')[1] })
            .GroupBy(m => m.Key)
            .ToDictionary(m => m.Key, m => string.Join(",", m.Select(p => p.Value)));

answered Sep 19, 2017 at 3:13

wittpeng

562 bronze badges

Comments

Antonín Lejsek · Accepted Answer · 2017-09-19 03:58:46Z

1

I am sad how nobody cares about performace. Wasteful allocations, wasteful calculations. I tested accepted answer against this code on strings with 50% key collisions:

char[] separatorArray = { ':' }; // do not create new array on every single item of the array
HashSet<string> dedupl = new HashSet<string>();

var res = array
    .Select(s => s.Split(separatorArray))
    .Where(x => dedupl.Add(x[0]))
    .ToDictionary(x => x[0], x => x[1]);

it is roughly 2,5x faster and uses half of the memory (I measured top memory usage).

answered Sep 19, 2017 at 3:58

Antonín Lejsek

6,1132 gold badges18 silver badges18 bronze badges

Collectives™ on Stack Overflow

C# - Convert delimited string array w/ duplicates to dictionary using LINQ

4 Answers 4

3 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related