SkipLastBenchmark.cs

# depends on BenchmarkDotNet

using System;
using System.Collections.Generic;
using System.Linq;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

namespace SkipLastBenchmark
{
    public static class Exts
    {
        static public IEnumerable<T> SkipLast1<T>(this IEnumerable<T> data, int count)
        {
            if (data == null || count < 0) yield break;

            Queue<T> queue = new Queue<T>(data.Take(count));

            foreach (T item in data.Skip(count))
            {
                queue.Enqueue(item);
                yield return queue.Dequeue();
            }
        }

        static public IEnumerable<T> SkipLast2<T>(this IEnumerable<T> data, int count)
        {
            if (data == null || count < 0)
                yield break;
                
            if (count == 0)
            {
                foreach (T item in data)
                yield return item;
            }
            else
            {
                T[] queue = data.Take(count).ToArray();
                int index = 0;

                foreach (T item in data.Skip(count))
                {
                    index %= count;
                    yield return queue[index];
                    queue[index] = item;
                    index++;
                }
            }
        }

        static public IEnumerable<T> SkipLast3<T>(this IEnumerable<T> source, int count)
        {
            if (source == null)
                throw new ArgumentNullException("Source Enumeration may not be null", nameof(source));
                
            if (count <= 0)
            {
                foreach (T item in source)
                    yield return item;
            }
            else
            {
                bool yielding = false;
                T[] buffer = new T[count];
                int index = 0;

                foreach (T item in source)
                {
                    if (index == count)
                    {
                        index = 0;
                        yielding = true;
                    }
                    
                    if (yielding)
                        yield return buffer[index];

                    buffer[index] = item;
                    index++;
                }
            }
        }

        static public IEnumerable<T> SkipLast4<T>(this IEnumerable<T> source, int count)
        {
            if (source == null)
                throw new ArgumentNullException("Source Enumeration may not be null", nameof(source));
                
            if (count <= 0)
            {
                foreach (T item in source)
                    yield return item;
            }
            else
            {
                T[] buffer = new T[count];

                using (var e = source.GetEnumerator())
                {
                    // initial filling of buffer
                    for (int i = 0; i < buffer.Length; i++)
                    {
                        if (!e.MoveNext())
                            yield break;

                        buffer[i] = e.Current;
                    }

                    int index = 0;
                    while (e.MoveNext())
                    {
                        yield return buffer[index];
                        buffer[index] = e.Current;
                        index = (index + 1) % count;
                    }
                }
            }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var summary = BenchmarkRunner.Run<Bench>();
        }
    }

    public class Bench
    {
        public IEnumerable<int> Lengths => new int[] { 0, 100, 100000 };
        public IEnumerable<int> Counts => new int[] { 0, 10, 1000 };

        [ParamsSource(nameof(Lengths))]
        public int Length { get; set; }

        [ParamsSource(nameof(Counts))]
        public int Count { get; set; }

        public IEnumerable<int> Array { get; set; }
        public IEnumerable<int> Range { get; set; }
        public IEnumerable<int> Thing { get; set; }

        [GlobalSetup]
        public void GlobalSetup()
        {
            Array = new int[Length];
            Range = Enumerable.Range(0, Length);
            Thing = MysteryRange(Length);
        }

        static IEnumerable<int> MysteryRange(int count)
        {
            for (int i = 0; i < count; i++)
                yield return i;
        }
        
        [GlobalCleanup]
        public void GlobalCleanup()
        {
            // nix
        }

        [Benchmark]
        public void SkipLastNetCoreArrays() { foreach (var a in Array.SkipLast(Count)); }
        [Benchmark]
        public void SkipLast1Arrays() { foreach (var a in Array.SkipLast1(Count)); }
        [Benchmark]
        public void SkipLast2Arrays() { foreach (var a in Array.SkipLast2(Count)); }
        [Benchmark]
        public void SkipLast3Arrays() { foreach (var a in Array.SkipLast3(Count)); }
        [Benchmark]
        public void SkipLast4Arrays() { foreach (var a in Array.SkipLast4(Count)); }
        
        [Benchmark]
        public void SkipLast1Ranges() { foreach (var a in Range.SkipLast1(Count)); }
        [Benchmark]
        public void SkipLast2Ranges() { foreach (var a in Range.SkipLast2(Count)); }
        [Benchmark]
        public void SkipLast3Ranges() { foreach (var a in Range.SkipLast3(Count)); }
        [Benchmark]
        public void SkipLast4Ranges() { foreach (var a in Range.SkipLast4(Count)); }
        
        [Benchmark]
        public void SkipLastNetCoreThings() { foreach (var a in Thing.SkipLast(Count)); }
        [Benchmark]
        public void SkipLast1Things() { foreach (var a in Thing.SkipLast1(Count)); }
        [Benchmark]
        public void SkipLast2Things() { foreach (var a in Thing.SkipLast2(Count)); }
        [Benchmark]
        public void SkipLast3Things() { foreach (var a in Thing.SkipLast3(Count)); }
        [Benchmark]
        public void SkipLast4Things() { foreach (var a in Thing.SkipLast4(Count)); }
    }
}

SkipLastBenchmark.Bench-20190706-113102

BenchmarkDotNet=v0.11.5, OS=Windows 7 SP1 (6.1.7601.0)
Intel Core i7-2670QM CPU 2.20GHz (Sandy Bridge), 1 CPU, 8 logical and 4 physical cores
Frequency=2143593 Hz, Resolution=466.5065 ns, Timer=TSC
.NET Core SDK=3.0.100-preview6-012264
  [Host]     : .NET Core 3.0.0-preview6-27804-01 (CoreCLR 4.700.19.30373, CoreFX 4.700.19.30308), 64bit RyuJIT
  DefaultJob : .NET Core 3.0.0-preview6-27804-01 (CoreCLR 4.700.19.30373, CoreFX 4.700.19.30308), 64bit RyuJIT

Legends

• Length : Value of the 'Length' parameter
• Count : Value of the 'Count' parameter
• Mean : Arithmetic mean of all measurements
• Error : Half of 99.9% confidence interval
• StdDev : Standard deviation of all measurements
• Median : Value separating the higher half of all measurements (50th percentile)

Method	Length	Count	Mean	Error	StdDev	Median
SkipLastNetCoreArrays	0	0	94.52 ns	0.8521 ns	0.7554 ns	94.65 ns
SkipLast1Arrays	0	0	192.17 ns	2.8857 ns	2.4097 ns	191.47 ns
SkipLast2Arrays	0	0	61.30 ns	0.9265 ns	0.8213 ns	61.22 ns
SkipLast3Arrays	0	0	59.16 ns	0.3548 ns	0.3319 ns	59.11 ns
SkipLast4Arrays	0	0	60.74 ns	0.2400 ns	0.2245 ns	60.81 ns
SkipLast1Ranges	0	0	110.22 ns	1.9719 ns	1.8445 ns	110.02 ns
SkipLast2Ranges	0	0	58.71 ns	1.1016 ns	0.8601 ns	58.37 ns
SkipLast3Ranges	0	0	56.39 ns	0.1652 ns	0.1465 ns	56.38 ns
SkipLast4Ranges	0	0	56.32 ns	0.6962 ns	0.5814 ns	56.17 ns
SkipLastNetCoreThings	0	0	98.44 ns	0.6445 ns	0.6029 ns	98.31 ns
SkipLast1Things	0	0	190.33 ns	0.9272 ns	0.7743 ns	190.28 ns
SkipLast2Things	0	0	77.45 ns	0.3684 ns	0.3446 ns	77.42 ns
SkipLast3Things	0	0	77.03 ns	0.3176 ns	0.2971 ns	77.00 ns
SkipLast4Things	0	0	77.51 ns	0.4102 ns	0.3837 ns	77.48 ns
SkipLastNetCoreArrays	0	10	77.06 ns	0.8803 ns	0.8235 ns	76.72 ns
SkipLast1Arrays	0	10	260.03 ns	0.7995 ns	0.7479 ns	260.21 ns
SkipLast2Arrays	0	10	237.88 ns	2.7745 ns	2.5952 ns	237.28 ns
SkipLast3Arrays	0	10	76.85 ns	1.5353 ns	1.7065 ns	76.19 ns
SkipLast4Arrays	0	10	77.31 ns	0.5970 ns	0.5584 ns	77.08 ns
SkipLast1Ranges	0	10	111.26 ns	0.3006 ns	0.2665 ns	111.21 ns
SkipLast2Ranges	0	10	90.45 ns	0.5031 ns	0.4201 ns	90.56 ns
SkipLast3Ranges	0	10	77.92 ns	2.2161 ns	1.9645 ns	77.09 ns
SkipLast4Ranges	0	10	77.07 ns	1.6838 ns	2.3049 ns	76.04 ns
SkipLastNetCoreThings	0	10	89.39 ns	2.1110 ns	2.5130 ns	88.54 ns
SkipLast1Things	0	10	268.89 ns	1.0638 ns	0.8305 ns	269.06 ns
SkipLast2Things	0	10	249.74 ns	0.9372 ns	0.8308 ns	249.38 ns
SkipLast3Things	0	10	92.70 ns	0.2643 ns	0.2472 ns	92.64 ns
SkipLast4Things	0	10	119.01 ns	2.4273 ns	5.7688 ns	118.68 ns
SkipLastNetCoreArrays	0	1000	100.32 ns	0.3806 ns	0.3374 ns	100.18 ns
SkipLast1Arrays	0	1000	331.89 ns	1.2132 ns	1.1348 ns	331.52 ns
SkipLast2Arrays	0	1000	238.13 ns	0.4682 ns	0.4379 ns	238.15 ns
SkipLast3Arrays	0	1000	443.05 ns	4.5160 ns	4.2243 ns	443.37 ns
SkipLast4Arrays	0	1000	403.55 ns	2.5047 ns	2.0915 ns	403.26 ns
SkipLast1Ranges	0	1000	136.56 ns	3.5703 ns	9.8932 ns	140.41 ns
SkipLast2Ranges	0	1000	115.09 ns	0.3782 ns	0.3353 ns	115.11 ns
SkipLast3Ranges	0	1000	404.82 ns	8.1296 ns	8.3485 ns	407.10 ns
SkipLast4Ranges	0	1000	406.45 ns	7.8010 ns	8.3470 ns	406.22 ns
SkipLastNetCoreThings	0	1000	119.97 ns	1.0089 ns	0.9437 ns	119.49 ns
SkipLast1Things	0	1000	337.43 ns	1.6595 ns	1.5523 ns	336.69 ns
SkipLast2Things	0	1000	317.76 ns	1.2803 ns	1.1976 ns	317.47 ns
SkipLast3Things	0	1000	432.27 ns	8.3622 ns	8.2128 ns	429.90 ns
SkipLast4Things	0	1000	424.42 ns	3.3114 ns	3.0975 ns	424.25 ns
SkipLastNetCoreArrays	100	0	1,496.12 ns	3.9343 ns	3.6801 ns	1,496.26 ns
SkipLast1Arrays	100	0	3,577.88 ns	7.8219 ns	7.3167 ns	3,577.47 ns
SkipLast2Arrays	100	0	1,616.91 ns	8.4080 ns	6.5644 ns	1,615.73 ns
SkipLast3Arrays	100	0	2,109.04 ns	5.6291 ns	5.2655 ns	2,106.44 ns
SkipLast4Arrays	100	0	2,078.98 ns	11.6700 ns	10.9162 ns	2,078.00 ns
SkipLast1Ranges	100	0	3,383.20 ns	7.0656 ns	6.6091 ns	3,383.85 ns
SkipLast2Ranges	100	0	2,046.10 ns	5.7535 ns	5.3818 ns	2,045.26 ns
SkipLast3Ranges	100	0	2,153.31 ns	5.1561 ns	4.8230 ns	2,151.37 ns
SkipLast4Ranges	100	0	2,133.00 ns	19.8706 ns	17.6147 ns	2,128.18 ns
SkipLastNetCoreThings	100	0	1,740.53 ns	51.5063 ns	65.1389 ns	1,727.84 ns
SkipLast1Things	100	0	3,838.19 ns	16.2289 ns	15.1806 ns	3,836.69 ns
SkipLast2Things	100	0	1,744.54 ns	6.9930 ns	6.5413 ns	1,745.29 ns
SkipLast3Things	100	0	1,705.52 ns	4.6355 ns	4.3360 ns	1,705.78 ns
SkipLast4Things	100	0	1,695.68 ns	4.6860 ns	4.3833 ns	1,694.51 ns
SkipLastNetCoreArrays	100	10	2,733.73 ns	5.2760 ns	4.9352 ns	2,733.49 ns
SkipLast1Arrays	100	10	3,484.25 ns	6.9189 ns	6.4720 ns	3,484.64 ns
SkipLast2Arrays	100	10	2,781.23 ns	8.5018 ns	7.9526 ns	2,783.27 ns
SkipLast3Arrays	100	10	2,251.64 ns	4.6655 ns	4.3641 ns	2,251.99 ns
SkipLast4Arrays	100	10	2,114.38 ns	6.6747 ns	6.2435 ns	2,115.72 ns
SkipLast1Ranges	100	10	3,367.97 ns	83.8485 ns	243.2597 ns	3,467.37 ns
SkipLast2Ranges	100	10	2,603.48 ns	5.3081 ns	4.9652 ns	2,602.52 ns
SkipLast3Ranges	100	10	2,301.90 ns	7.6143 ns	6.7499 ns	2,302.60 ns
SkipLast4Ranges	100	10	2,109.45 ns	8.1434 ns	7.6174 ns	2,108.79 ns
SkipLastNetCoreThings	100	10	2,758.94 ns	14.5202 ns	12.8718 ns	2,761.45 ns
SkipLast1Things	100	10	3,741.48 ns	15.7257 ns	14.7098 ns	3,743.52 ns
SkipLast2Things	100	10	3,268.22 ns	69.6281 ns	80.1838 ns	3,241.15 ns
SkipLast3Things	100	10	2,317.00 ns	19.0728 ns	16.9076 ns	2,317.91 ns
SkipLast4Things	100	10	2,721.31 ns	54.2785 ns	117.9970 ns	2,745.69 ns
SkipLastNetCoreArrays	100	1000	2,175.95 ns	14.5384 ns	12.8879 ns	2,172.64 ns
SkipLast1Arrays	100	1000	2,750.66 ns	14.8926 ns	13.9305 ns	2,754.45 ns
SkipLast2Arrays	100	1000	927.77 ns	2.2752 ns	2.1282 ns	927.14 ns
SkipLast3Arrays	100	1000	1,577.69 ns	3.1901 ns	2.8279 ns	1,576.82 ns
SkipLast4Arrays	100	1000	1,203.56 ns	7.5855 ns	7.0955 ns	1,201.97 ns
SkipLast1Ranges	100	1000	1,234.57 ns	8.4862 ns	7.5228 ns	1,233.19 ns
SkipLast2Ranges	100	1000	300.37 ns	3.4852 ns	3.2601 ns	300.53 ns
SkipLast3Ranges	100	1000	2,017.32 ns	26.7232 ns	24.9969 ns	2,007.69 ns
SkipLast4Ranges	100	1000	1,533.77 ns	15.7411 ns	14.7243 ns	1,529.84 ns
SkipLastNetCoreThings	100	1000	2,244.49 ns	12.9202 ns	12.0855 ns	2,244.29 ns
SkipLast1Things	100	1000	3,566.32 ns	42.8585 ns	40.0898 ns	3,547.28 ns
SkipLast2Things	100	1000	2,709.74 ns	4.9709 ns	4.4065 ns	2,709.41 ns
SkipLast3Things	100	1000	1,808.90 ns	4.9616 ns	4.3983 ns	1,809.03 ns
SkipLast4Things	100	1000	1,507.32 ns	5.7221 ns	4.4674 ns	1,506.75 ns
SkipLastNetCoreArrays	100000	0	1,346,506.72 ns	4,920.2559 ns	4,602.4105 ns	1,347,498.47 ns
SkipLast1Arrays	100000	0	3,356,476.68 ns	8,380.4380 ns	7,429.0400 ns	3,355,003.36 ns
SkipLast2Arrays	100000	0	1,491,103.31 ns	2,673.8534 ns	2,501.1241 ns	1,491,366.51 ns
SkipLast3Arrays	100000	0	1,498,072.45 ns	3,167.3327 ns	2,962.7250 ns	1,498,109.44 ns
SkipLast4Arrays	100000	0	1,536,940.43 ns	3,669.2302 ns	3,432.2002 ns	1,538,079.12 ns
SkipLast1Ranges	100000	0	3,106,530.98 ns	61,504.2603 ns	156,547.9799 ns	3,145,387.06 ns
SkipLast2Ranges	100000	0	1,938,133.62 ns	2,214.3457 ns	2,071.3004 ns	1,938,124.81 ns
SkipLast3Ranges	100000	0	1,950,613.10 ns	22,745.7191 ns	20,163.4875 ns	1,940,924.31 ns
SkipLast4Ranges	100000	0	1,499,284.67 ns	9,054.9129 ns	8,469.9712 ns	1,495,816.54 ns
SkipLastNetCoreThings	100000	0	1,483,145.64 ns	11,652.9480 ns	10,330.0349 ns	1,486,023.55 ns
SkipLast1Things	100000	0	3,616,311.49 ns	30,812.2704 ns	28,821.8169 ns	3,612,307.19 ns
SkipLast2Things	100000	0	1,650,822.57 ns	29,344.2411 ns	24,503.7703 ns	1,644,940.99 ns
SkipLast3Things	100000	0	2,022,209.61 ns	2,015.8980 ns	1,787.0411 ns	2,021,891.42 ns
SkipLast4Things	100000	0	2,020,873.22 ns	3,097.1151 ns	2,897.0434 ns	2,020,964.33 ns
SkipLastNetCoreArrays	100000	10	3,343,891.81 ns	29,999.5397 ns	26,593.8106 ns	3,329,758.25 ns
SkipLast1Arrays	100000	10	4,191,115.98 ns	16,150.3103 ns	15,107.0102 ns	4,192,471.76 ns
SkipLast2Arrays	100000	10	2,757,554.50 ns	54,654.9204 ns	95,723.6842 ns	2,715,102.27 ns
SkipLast3Arrays	100000	10	2,267,643.96 ns	17,906.8654 ns	16,750.0930 ns	2,271,915.66 ns
SkipLast4Arrays	100000	10	2,117,668.33 ns	14,020.3580 ns	13,114.6516 ns	2,121,328.83 ns
SkipLast1Ranges	100000	10	2,575,748.16 ns	16,771.2296 ns	15,687.8186 ns	2,577,896.52 ns
SkipLast2Ranges	100000	10	2,016,961.93 ns	9,553.5107 ns	8,468.9384 ns	2,016,547.10 ns
SkipLast3Ranges	100000	10	2,058,685.76 ns	10,114.6655 ns	9,461.2644 ns	2,060,998.24 ns
SkipLast4Ranges	100000	10	2,081,034.33 ns	17,464.5716 ns	15,481.8878 ns	2,077,674.94 ns
SkipLastNetCoreThings	100000	10	2,626,660.54 ns	14,888.3192 ns	13,926.5430 ns	2,627,271.49 ns
SkipLast1Things	100000	10	3,493,533.79 ns	14,802.4900 ns	13,846.2583 ns	3,491,168.58 ns
SkipLast2Things	100000	10	3,782,114.69 ns	7,354.0797 ns	6,879.0107 ns	3,783,145.14 ns
SkipLast3Things	100000	10	2,784,520.01 ns	3,266.7998 ns	3,055.7666 ns	2,783,871.88 ns
SkipLast4Things	100000	10	2,805,656.20 ns	53,084.6968 ns	47,058.2010 ns	2,786,810.33 ns
SkipLastNetCoreArrays	100000	1000	3,219,414.11 ns	3,359.1070 ns	3,142.1107 ns	3,218,225.85 ns
SkipLast1Arrays	100000	1000	4,018,749.86 ns	7,619.8173 ns	7,127.5818 ns	4,019,029.76 ns
SkipLast2Arrays	100000	1000	3,543,975.41 ns	10,935.6161 ns	10,229.1821 ns	3,541,155.84 ns
SkipLast3Arrays	100000	1000	2,891,986.82 ns	7,155.7567 ns	6,693.4992 ns	2,891,807.99 ns
SkipLast4Arrays	100000	1000	2,135,899.99 ns	10,700.8717 ns	10,009.6020 ns	2,136,561.36 ns
SkipLast1Ranges	100000	1000	2,455,941.77 ns	8,165.2179 ns	7,637.7499 ns	2,455,427.64 ns
SkipLast2Ranges	100000	1000	2,114,850.58 ns	10,742.1909 ns	10,048.2521 ns	2,111,093.02 ns
SkipLast3Ranges	100000	1000	2,125,203.87 ns	11,053.4244 ns	10,339.3801 ns	2,125,512.81 ns
SkipLast4Ranges	100000	1000	2,089,056.42 ns	8,764.2002 ns	8,198.0383 ns	2,085,285.74 ns
SkipLastNetCoreThings	100000	1000	2,522,630.93 ns	7,186.8495 ns	6,722.5834 ns	2,523,111.17 ns
SkipLast1Things	100000	1000	3,354,383.66 ns	14,250.2726 ns	13,329.7138 ns	3,353,541.88 ns
SkipLast2Things	100000	1000	2,953,928.92 ns	6,367.2951 ns	5,955.9718 ns	2,952,461.12 ns
SkipLast3Things	100000	1000	2,241,011.91 ns	10,903.9357 ns	10,199.5482 ns	2,240,134.90 ns
SkipLast4Things	100000	1000	2,740,062.68 ns	56,549.0378 ns	165,848.5390 ns	2,787,877.28 ns