Question

For example, I have a sequence of integers

1122211121

I’d like to get some dictionary/anonymous class showing:

item | count
1    | 2
2    | 3
1    | 3
2    | 1
1    | 1

Answer 1

        var test = new[] { 1, 2, 2, 2, 2, 1, 1, 3 };
        int previous = test.First();
        int idx = 0;
        test.Select(x =>
                x == previous ?
                new { orig = x, helper = idx } :
                new { orig = previous = x, helper = ++idx })
            .GroupBy(x => x.helper)
            .Select(group => new { number = group.First().orig, count = group.Count() });

initialization of previous and idx could be done in let clause if you want to be even more Linqy.

       from whatever in new[] { "i want to use linq everywhere" }
       let previous = test.First()
       let idx = 0
       from x in test
       ...

Functional programming is nice, but imho this is a case where in C# I would surely choose rather procedural approach.