.NET 9 new LINQ CountBy compared to existing approaches benchmarks

CountByDotnet9.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Columns;
using BenchmarkDotNet.Configs;
using BenchmarkDotNet.Environments;
using BenchmarkDotNet.Jobs;
using BenchmarkDotNet.Reports;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Benchmarks
{
    [Config(typeof(Config))]
    [HideColumns(Column.Job, Column.RatioSD, Column.AllocRatio)]
    [MemoryDiagnoser]
    [ReturnValueValidator(true)]
    public class CountByDotnet9
    {
        private static int SequenceLength = 100000;
        private static int GroupsCount = 100;

        private static Random random = new(42);
        private static readonly int[] Seq = Enumerable
            .Range(0, SequenceLength)
            .Select(_ => random.Next(0, GroupsCount)).ToArray();

        [Benchmark]
        public IDictionary<int, int> Grouping() =>
          Seq
            .GroupBy(x => x)
            .ToDictionary(x => x.Key, x => x.Count());

        [Benchmark]
        public IDictionary<int, int> LookupDict() =>
          Seq
            .ToLookup(x => x)
            .ToDictionary(x => x.Key, x => x.Count());

        [Benchmark(Baseline = true)]
        public IDictionary<int, int> Counting() =>
          Seq
            .CountBy(x => x)
            .ToDictionary(x => x.Key, x => x.Value);

        private class Config : ManualConfig
        {
            public Config()
            {
                AddJob(Job.Default.WithId(".NET 9").WithRuntime(CoreRuntime.Core90));

                SummaryStyle =
                    SummaryStyle.Default.WithRatioStyle(RatioStyle.Percentage);
            }
        }
    }
}