Chunking a Collection into Groups of Three

Raw data for a LINQ query doesn’t always come in the form you want.  Recently, I had some data like this:

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string[] source = new [] {
"EW",
"Eric",
"8:00",
"DW",
"Dave",
"9:00",
"JA",
"Jim",
"8:00"
};

You want to transform the above collection of strings into a collection of anonymous objects that are easier to work on, so you need to write a query that operates on groups of three.  To solve this problem, you can take advantage that the Select extension method has an overload that passes an index number to the selection function:

string[] source = new [] {
"EW",
"Eric",
"8:00",
"DW",
"Dave",
"9:00",
"JA",
"Jim",
"8:00"
};
var people = source
.Select
(
(s, i) =>
new
{
Value = s,
Chunk = i / 3
}
)
.GroupBy(x => x.Chunk)
.Select
(
g =>
new
{
Initials = g.First().Value,
Name = g.Skip(1).First().Value,
Time = g.Skip(2).First().Value
}
);
foreach (var p in people)
Console.WriteLine(p);

This produces the following output:

{ Initials = EW, Name = Eric, Time = 8:00 }
{ Initials = DW, Name = Dave, Time = 9:00 }
{ Initials = JA, Name = Jim, Time = 8:00 }

This new collection is a whole lot easier to work with.

Comments

• Anonymous
  August 19, 2008
  Excellent. Didn't know you could do that.

• Anonymous
  August 22, 2008
  The comment has been removed

• Anonymous
  August 22, 2008
  Samual, Your approach using an interator is fine too.  It has an advantage - the approach that I showed creates more short-lived objects on the heap.  Sometimes I am writing ad-hoq LINQ transforms for one reason or another, in which case I would use the above approach.  If I were making a library that would be used by many people, I would optimize using an approach similar to yours. -Eric

• Anonymous
  September 29, 2008
  Transforming Open XML documents using XSLT is an interesting scenario, but before we can do so, we need