Using Linq to group, order and concatenate strings - vb.net

Question

Suppose I have the following data
Key ID Data
A 1 Hello
A 2 World
B 2 Bar
B 1 Foo
I am looking to produce the result
A HelloWorld
B FooBar
I am struggling to get the syntax quite right - I was trying to use Aggregate, but I wasn't sure if I could (or should) use SelectMany
I'd be grateful of any help.
Dim data = result.Rows.
GroupBy(Function(r) r.Key).
Select(Function(g) g.OrderBy(Function(s) s.ID)).
Aggregate(New StringBuilder, Function(cur, nxt)
cur.Append(nxt.First.Data))
Thanks
Simon

Answer 1

I think this (C#) should work:
var data = from r in result.Rows
group r by r.Item("Key").ToString() into g
select new {
g.Key,
Joined = string.Join("", g.OrderBy(s => s.Item("ID"))
.Select(s => s.Item("Data")))
};

Answer 2

Dim result = result.Rows.GroupBy(Function(r) r.Key).Select(Function(g) New With { _
g.Key, _
String.Join("", g.OrderBy(Function(r) r.ID)) _
})

Answer 3

Here's an alternative implementation:
var source = new Item[]
{
new Item { Key = "A", ID = 1, Data = "Hello" },
new Item { Key = "A", ID = 2, Data = "World" },
new Item { Key = "B", ID = 2, Data = "Bar" },
new Item { Key = "B", ID = 1, Data = "Foo" }
};
var results = source
.GroupBy(item => item.Key)
.Select(group => group
.OrderBy(item => item.ID)
.Aggregate(new Item(), (result, item) =>
{
result.Key = item.Key;
result.Data += item.Data;
return result;
}));

Answer 4

You don't want to Aggregate the groups. You want to aggregage the elements of each group unto itself.
If you want the query to do it, then
Dim data = result.Rows
.GroupBy( )
.Select(Function(g) g
.OrderBy( )
.Aggregate( )
)
If that anonymous function starts getting too hairy to write, just make a method that accepts an IGrouping<int, Row> and turns it into what you want. Then call it like:
Dim data = result.Rows
.GroupBy( )
.Select( myMethod )