Group by in a dictionary<string, IList<string>>

January 7, 2022

I have a list of items "listItems", like this

Id Code Value
1  'a'  '1'
2  'a'  '2'
3  'b'  'x'
4  'b'  'y'

and want to obtain a dictionary,

'a' => '1', '2'
'b' => 'x', 'y'

I tried

listItems.ToDictionary(x => x.Code, x => x.Value), but this returns a Dictionary<string, string>, I would like to have a Dictionary<string, IList<string>>

>Solution :

you can group by first

// gives Dictionary<string,IEnumerable<YourObject>>
listItems.GroupBy(x => x.Code).ToDictionary(x => x.Key);

you could project the values in the dictionary if need be:

// gives Dictionary<string,List<string>>
listItems.GroupBy(x => x.Code)
         .ToDictionary(
             x => x.Key, 
             x => x.Select(y => y.Value).ToList()
         );