LINQ to find series of consecutive numbers

algorithm, c#, linq, list

Solution

A linqish way can be writing an extension method `GroupWhile` like below (All checks omitted. not optimized to understand easily.)

int[] list = new int[] { 1, 2, 3, 5, 7, 8 };
var result = list.GroupWhile((x, y) => y - x == 1)
                 .Select(x => new {i = x.First(), len = x.Count()  })
                 .ToList();

public static IEnumerable<IEnumerable<T>> GroupWhile<T>(this IEnumerable<T> seq, Func<T,T,bool> condition)
{
    T prev = seq.First();
    List<T> list = new List<T>() { prev };

    foreach(T item in seq.Skip(1))
    {
        if(condition(prev,item)==false)
        {
            yield return list;
            list = new List<T>();
        }
        list.Add(item);
        prev = item;
    }

    yield return list;
}

TODO: use `IGrouping` :)

Problem

I have a list of integers. I want to find all runs of consecutive numbers on that list, defined by the start index and length. So for example, for input list of `[1,2,3,5,7,8]`, the output would be `[{1,3}, {5,1}, {7,2}]`. This is easy enough to do using a loop, something like this (untested pseudocode): ``` for(i=1, i < maxNum; i++) { number = list[i]; previousNumber = list[i-1]; if(number - previousNumber == 1) { runLength++; } else { result.Add(startingNumber, runLength); runLength = 1; startingNumber = number; } } ``` But I thought it would be possible to do using LINQ. Any ideas how to do that?

Original source