ScanBy

scanby.cs

using System;
using System.Linq;


static class Program
{
    public static IEnumerable<TAcc> ScanBy<T, TKey, TAcc>(this IEnumerable<T> source, Func<T, TKey> keyFunc, Func<TKey, T, TAcc> seedFunc, Func<TAcc, T, TAcc> aggregateFunc)
    {
        TAcc acc = default!;
        TKey key = default!;
        bool pending = false;
        EqualityComparer<TKey> comparer = EqualityComparer<TKey>.Default;
        foreach (var item in source)
        {
            if (!pending)
            {
                key = keyFunc(item);
                acc = seedFunc(key, item);
                pending = true;
                continue;
            }
            TKey currentKey = keyFunc(item);
            if (!comparer.Equals(key, currentKey))
            {
                yield return acc;
                key = currentKey;
                acc = seedFunc(key, item);
            }
            else
                acc = aggregateFunc(acc, item);
        }
        if (pending)
            yield return acc;
    }


    public static void Main()
    {
        bool[] bits = [true,true,true,false,true,false,false];
        // RLE
        // (true, 3), (false, 1), (true, 1), (false, 2)
        var rle = bits.ScanBy(x => x, (key, item) => (Bit: key, Sum: 1), 
                              (acc, item) => (acc.Bit, acc.Sum + 1));
        foreach (var (key, count) in rle)
            Console.WriteLine($"({key}, {count})");
    }
}