LINQ query — Data aggregation (Group Adjacent)

Question

Let\'s take a class called Cls:

public class Cls
{
    public int SequenceNumber { get; set; }
    public int Value { get; set; }
}

Answer 1

You can do it like this:

var all = new [] {
    new Cls(1, 9)
,   new Cls(2, 9)
,   new Cls(3, 15)
,   new Cls(4, 15)
,   new Cls(5, 15)
,   new Cls(6, 30)
,   new Cls(7, 9)
};
var f = all.First();
var res = all.Skip(1).Aggregate(
    new List {new Run {From = f.SequenceNumber, To = f.SequenceNumber, Value = f.Value} }
,   (p, v) => {
    if (v.Value == p.Last().Value) {
        p.Last().To = v.SequenceNumber;
    } else {
        p.Add(new Run {From = v.SequenceNumber, To = v.SequenceNumber, Value = v.Value});
    }
    return p;
});
foreach (var r in res) {
    Console.WriteLine("{0} - {1} : {2}", r.From, r.To, r.Value);
}

The idea is to use Aggregate creatively: starting with a list consisting of a single Run, examine the content of the list we've got so far at each stage of aggregation (the if statement in the lambda). Depending on the last value, either continue the old run, or start a new one.

Here is a demo on ideone.