LINQ Dictionary Non-Distinct Values

Question

I am struggeling a little with trying to write the LINQ query to do the following,

public class MyClass
{
    public int ID {get; set;}
    public int Name {get; set;}
    public IEnumerable<string> SomeIEnumerable {get; set;}
}

I am trying to create the object using LINQ from a DB query that would return something as follows,

ID    Name     SomeString
0     NameA    "MyValue"
1     NameB    "Value1"
1     NameB    "Value2"
2     NameC    "Value"

The LINQ is pretty easy to write as well,

from DataRow row in dataSet.Tables[0].Rows
select new MyClass
{
    ID = (int)row["ID"],
    Name = row["Name"].ToString(),
    SomeIEnumerable = new List<string>{ row["SomeString"].ToString() }
};

The tricky part is how do I turn this into a Dictionary where dictionary[1].SomeIEnumerable = {"Value1", "Value2"}

A simple ToDictionary would throw an ArgumentException

The main issue here, is how do I handle the fact that the keyis not distinct, and be able to lookup in the temporary dictionary the existing value to add to it the values I am interested in.

Keys needs to distinct, for that you can select only distinct rows by id. — Asif Mushtaq, May 15 '12 at 11:02
Your “pretty easy” LINQ wouldn't work, because `Add()` returns `void`. But something like `new List{ (string)row["SomeString"] }` would. — svick, May 15 '12 at 11:34

score 3 · Answer 1 · edited May 15 '12 at 13:37

3

Instead of calling ToDictionary, call ToLookup. :)

edited May 15 '12 at 13:37

Roman

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answered May 15 '12 at 11:03

leppie

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score 3 · Accepted Answer · answered May 15 '12 at 11:22

3

You can also your grouping, and then use IGrouping to retrieve the list of items in the group

Sample code

    var simulatedData = Enumerable.Range(0,10).Select(x=> new {Key=x%3+1, Index=x}); 
    var dict = simulatedData.GroupBy(x=>x.Key).ToDictionary(x=>x.Key, x=>x.Select(t=>t.Index));

answered May 15 '12 at 11:22

Tilak

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Thank you, will paste me answer in a second – M Afifi May 15 '12 at 11:41

score 1 · Answer 3 · answered May 15 '12 at 11:44

Answer thanks to @Tilak is,

from DataRow row in dataSet.Tables[0].Rows
group row by new
{
    ID = (int) row["ID"],
    Name = row["Name].ToString()
} into rowGroup
select new MyClass
{
    ID = rowGroup.Key.ID,
    Name = rowGroup.Key.Name,
    SomeIEnumerable =
        from row in rowGroup
        select row["SomeString"].ToString()
};

LINQ Dictionary Non-Distinct Values

3 Answers3