如何确定c＃中字符串列表中的重复项？
我想知道如何确定以下重复项，并使用重复项填充新的字符串列表？
List<string> test = new List<string>();
我正在考虑这些问题，但收到编译错误，说我无法将 - 运算符应用于字符串列表。
List<string> namesCollisions = test - test.Distinct().ToList();
所以我按照建议尝试了以下操作，即使PROGRAM3列出两次，列表也是空的
3 个答案:
答案 0 :(得分：7)
基准
- 我对4种算法进行了基准测试
- 在64位
on both。Net Framework 4.7.1` - 每次测试运行1000次并平均
- 我缩放了每个数据集。
- 在每次测试之前，框架都会执行
GC.Collect和GC.WaitForPendingFinalizers - 和1次隔离测试以验证结果
我使用了4批输入数据
<强>输入
public static List<string> ListofSimpleString(int scale)
{
return Enumerable.Range(0, scale)
.Select(x => Enumerable.Range(0,10).Select(y => (char)_rand.Next(255)).ToString())
.ToList();
}
public static List<string> ListofSimpleString2(int scale)
{
return Enumerable.Range(0, scale)
.Select(x => Enumerable.Range(0, 10).Select(y => (char)_rand.Next(48,95)).ToString())
.ToList();
}
public static List<string> ListofSimpleString4(int scale)
{
return Enumerable.Range(0, scale)
.Select(x => _rand.Next(10).ToString())
.ToList();
}
public static List<string> ListofSimpleString5(int scale)
{
return Enumerable.Range(0, scale)
.Select(x => "duplicate value")
.ToList();
}
结果
Mode : Release (64Bit)
Test Framework : .NET Framework 4.7.1
Operating System : Microsoft Windows 10 Pro
Version : 10.0.17134
CPU Name : Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz
Description : Intel64 Family 6 Model 42 Stepping 7
Cores (Threads) : 4 (8) : Architecture : x64
Clock Speed : 3401 MHz : Bus Speed : 100 MHz
L2Cache : 1 MB : L3Cache : 8 MB
Benchmarks Runs : Inputs (4) * Scales (5) * Benchmarks (4) * Runs (10) = 800
测试1
--- 10 Random ascii chars -----------------------------------------------------------------------
| Value | Average | Fastest | Cycles | Garbage | Test | Gain |
--- Scale 10,000 ----------------------------------------------------------------- Time 0.099 ---
| Dictionary | 1.298 ms | 1.040 ms | 4,180,070 | 8.000 KB | N/A | 43.71 % |
| GroupByCount | 1.315 ms | 1.128 ms | 4,473,950 | 264.242 KB | N/A | 42.98 % |
| GroupBySkipAny | 1.387 ms | 1.097 ms | 4,622,163 | 264.242 KB | N/A | 39.88 % |
| HashSet | 2.306 ms | 2.010 ms | 7,842,618 | 8.000 KB | Base | 0.00 % |
--- Scale 100,000 ---------------------------------------------------------------- Time 0.656 ---
| Dictionary | 11.599 ms | 11.090 ms | 39,514,786 | 8.000 KB | N/A | 48.72 % |
| GroupByCount | 12.469 ms | 12.172 ms | 42,491,474 | 2.008 MB | N/A | 44.88 % |
| GroupBySkipAny | 12.834 ms | 12.490 ms | 43,703,545 | 2.008 MB | N/A | 43.26 % |
| HashSet | 22.620 ms | 22.171 ms | 77,091,768 | 8.000 KB | Base | 0.00 % |
--- Scale 1,000,000 -------------------------------------------------------------- Time 6.502 ---
| Dictionary | 116.635 ms | 114.583 ms | 397,153,297 | 8.000 KB | N/A | 50.92 % |
| GroupBySkipAny | 130.604 ms | 128.622 ms | 444,500,775 | 16.008 MB | N/A | 45.04 % |
| GroupByCount | 133.642 ms | 128.416 ms | 455,399,304 | 16.008 MB | N/A | 43.76 % |
| HashSet | 237.646 ms | 231.029 ms | 809,489,660 | 8.000 KB | Base | 0.00 % |
--- Scale 10,000,000 ------------------------------------------------------------- Time 5.844 ---
| Dictionary | 1,169.275 ms | 1,163.115 ms | 3,984,243,078 | 8.000 KB | N/A | 50.76 % |
| GroupBySkipAny | 1,353.768 ms | 1,345.292 ms | 4,608,323,709 | 256.009 MB | N/A | 43.00 % |
| GroupByCount | 1,358.509 ms | 1,344.632 ms | 4,627,402,507 | 256.009 MB | N/A | 42.80 % |
| HashSet | 2,374.831 ms | 2,334.440 ms | 8,089,227,303 | 8.000 KB | Base | 0.00 % |
--- Scale 100,000,000 ------------------------------------------------------------ Time 8.679 ---
| Dictionary | 11,751.858 ms | 11,656.590 ms | 40,027,059,699 | 8.000 KB | N/A | 52.24 % |
| GroupBySkipAny | 13,585.036 ms | 13,346.376 ms | 46,230,547,515 | 2.000 GB | N/A | 44.79 % |
| GroupByCount | 13,891.448 ms | 13,664.273 ms | 47,215,273,015 | 2.000 GB | N/A | 43.54 % |
| HashSet | 24,605.782 ms | 24,440.468 ms | 83,658,042,598 | 8.000 KB | Base | 0.00 % |
-------------------------------------------------------------------------------------------------
测试2
--- 10 Random printable ascii chars -------------------------------------------------------------
| Value | Average | Fastest | Cycles | Garbage | Test | Gain |
--- Scale 10,000 ----------------------------------------------------------------- Time 0.259 ---
| Dictionary | 1.087 ms | 1.052 ms | 3,654,669 | 8.000 KB | N/A | 50.38 % |
| GroupByCount | 1.182 ms | 1.133 ms | 4,020,552 | 264.211 KB | N/A | 46.07 % |
| GroupBySkipAny | 1.300 ms | 1.163 ms | 4,415,126 | 264.211 KB | N/A | 40.67 % |
| HashSet | 2.191 ms | 2.024 ms | 7,462,586 | 8.000 KB | Base | 0.00 % |
--- Scale 100,000 ---------------------------------------------------------------- Time 0.758 ---
| Dictionary | 12.033 ms | 11.333 ms | 40,839,598 | 8.000 KB | N/A | 48.66 % |
| GroupBySkipAny | 12.821 ms | 12.616 ms | 43,599,424 | 2.008 MB | N/A | 45.30 % |
| GroupByCount | 12.903 ms | 12.643 ms | 43,879,671 | 2.008 MB | N/A | 44.95 % |
| HashSet | 23.438 ms | 22.309 ms | 79,514,592 | 8.000 KB | Base | 0.00 % |
--- Scale 1,000,000 -------------------------------------------------------------- Time 6.687 ---
| Dictionary | 119.383 ms | 116.696 ms | 406,335,788 | 8.000 KB | N/A | 51.02 % |
| GroupBySkipAny | 134.819 ms | 131.747 ms | 458,589,071 | 16.008 MB | N/A | 44.68 % |
| GroupByCount | 139.834 ms | 132.961 ms | 476,092,342 | 16.008 MB | N/A | 42.63 % |
| HashSet | 243.722 ms | 239.580 ms | 829,409,546 | 8.000 KB | Base | 0.00 % |
--- Scale 10,000,000 ------------------------------------------------------------- Time 8.579 ---
| Dictionary | 1,237.373 ms | 1,213.387 ms | 4,203,352,967 | 8.000 KB | N/A | 49.48 % |
| GroupByCount | 1,404.209 ms | 1,385.300 ms | 4,778,762,566 | 256.009 MB | N/A | 42.67 % |
| GroupBySkipAny | 1,423.058 ms | 1,384.701 ms | 4,838,714,809 | 256.009 MB | N/A | 41.90 % |
| HashSet | 2,449.190 ms | 2,381.713 ms | 8,334,623,472 | 8.000 KB | Base | 0.00 % |
--- Scale 100,000,000 ----------------------------------------------------------- Time 59.573 ---
| Dictionary | 12,126.807 ms | 11,692.415 ms | 41,233,771,464 | 8.000 KB | N/A | 49.00 % |
| GroupByCount | 13,289.256 ms | 13,062.683 ms | 45,292,203,200 | 2.000 GB | N/A | 44.12 % |
| GroupBySkipAny | 13,760.635 ms | 13,261.366 ms | 46,825,002,767 | 2.000 GB | N/A | 42.13 % |
| HashSet | 23,780.270 ms | 22,785.622 ms | 80,971,187,805 | 8.000 KB | Base | 0.00 % |
-------------------------------------------------------------------------------------------------
测试3
--- Random number between 0 and 10 ------------------------------------------------------------
| Value | Average | Fastest | Cycles | Garbage | Test | Gain |
--- Scale 10,000 --------------------------------------------------------------- Time 0.224 ---
| Dictionary | 0.397 ms | 0.387 ms | 1,349,447 | 8.000 KB | N/A | 50.59 % |
| GroupBySkipAny | 0.495 ms | 0.490 ms | 1,683,949 | 200.563 KB | N/A | 38.38 % |
| GroupByCount | 0.506 ms | 0.503 ms | 1,722,584 | 200.563 KB | N/A | 36.97 % |
| HashSet | 0.803 ms | 0.786 ms | 2,734,083 | 8.000 KB | Base | 0.00 % |
--- Scale 100,000 -------------------------------------------------------------- Time 0.459 ---
| Dictionary | 3.929 ms | 3.767 ms | 13,387,884 | 8.000 KB | N/A | 48.65 % |
| GroupBySkipAny | 5.195 ms | 4.873 ms | 17,699,816 | 2.510 MB | N/A | 32.09 % |
| GroupByCount | 5.233 ms | 4.904 ms | 17,825,215 | 2.510 MB | N/A | 31.60 % |
| HashSet | 7.650 ms | 7.444 ms | 26,081,151 | 8.000 KB | Base | 0.00 % |
--- Scale 1,000,000 ------------------------------------------------------------ Time 3.416 ---
| Dictionary | 39.934 ms | 38.031 ms | 136,107,565 | 8.000 KB | N/A | 47.61 % |
| GroupBySkipAny | 52.159 ms | 50.011 ms | 177,797,622 | 20.011 MB | N/A | 31.57 % |
| GroupByCount | 54.562 ms | 49.745 ms | 185,883,905 | 20.011 MB | N/A | 28.42 % |
| HashSet | 76.221 ms | 73.899 ms | 259,702,109 | 8.000 KB | Base | 0.00 % |
--- Scale 10,000,000 ---------------------------------------------------------- Time 33.643 ---
| Dictionary | 396.948 ms | 381.873 ms | 1,352,809,995 | 7.035 KB | N/A | 47.82 % |
| GroupByCount | 519.931 ms | 515.210 ms | 1,771,927,979 | 160.012 MB | N/A | 31.66 % |
| GroupBySkipAny | 537.953 ms | 516.127 ms | 1,833,424,578 | 160.013 MB | N/A | 29.29 % |
| HashSet | 760.781 ms | 751.582 ms | 2,592,592,185 | 8.000 KB | Base | 0.00 % |
--- Scale 100,000,000 --------------------------------------------------------- Time 43.701 ---
| Dictionary | 3,945.544 ms | 3,845.146 ms | 13,442,361,467 | 8.000 KB | N/A | 49.08 % |
| GroupByCount | 5,666.408 ms | 5,501.203 ms | 19,301,260,141 | 2.500 GB | N/A | 26.87 % |
| GroupBySkipAny | 5,688.156 ms | 5,536.729 ms | 19,370,101,611 | 2.500 GB | N/A | 26.59 % |
| HashSet | 7,748.656 ms | 7,605.495 ms | 26,399,373,179 | 7.315 KB | Base | 0.00 % |
-----------------------------------------------------------------------------------------------
测试4
--- All Duplicates ----------------------------------------------------------------------------
| Value | Average | Fastest | Cycles | Garbage | Test | Gain |
--- Scale 10,000 --------------------------------------------------------------- Time 0.957 ---
| Dictionary | 0.444 ms | 0.425 ms | 1,508,780 | 8.000 KB | N/A | 50.55 % |
| GroupBySkipAny | 0.561 ms | 0.543 ms | 1,912,069 | 264.211 KB | N/A | 37.44 % |
| GroupByCount | 0.566 ms | 0.544 ms | 1,927,506 | 264.211 KB | N/A | 36.93 % |
| HashSet | 0.897 ms | 0.876 ms | 3,058,602 | 8.000 KB | Base | 0.00 % |
--- Scale 100,000 -------------------------------------------------------------- Time 0.341 ---
| Dictionary | 4.342 ms | 4.195 ms | 14,764,603 | 8.000 KB | N/A | 56.79 % |
| GroupBySkipAny | 6.090 ms | 5.437 ms | 20,636,444 | 2.008 MB | N/A | 39.38 % |
| GroupByCount | 6.327 ms | 5.812 ms | 21,478,886 | 2.008 MB | N/A | 37.03 % |
| HashSet | 10.047 ms | 8.627 ms | 34,243,915 | 8.000 KB | Base | 0.00 % |
--- Scale 1,000,000 ------------------------------------------------------------ Time 2.962 ---
| Dictionary | 45.242 ms | 42.814 ms | 154,054,415 | 8.000 KB | N/A | 54.02 % |
| GroupBySkipAny | 58.574 ms | 53.289 ms | 199,411,629 | 16.008 MB | N/A | 40.47 % |
| GroupByCount | 63.450 ms | 54.705 ms | 215,792,787 | 16.008 MB | N/A | 35.52 % |
| HashSet | 98.396 ms | 85.450 ms | 335,093,581 | 8.000 KB | Base | 0.00 % |
--- Scale 10,000,000 ---------------------------------------------------------- Time 28.309 ---
| Dictionary | 432.955 ms | 424.321 ms | 1,474,860,339 | 8.000 KB | N/A | 49.97 % |
| GroupByCount | 600.265 ms | 581.515 ms | 2,044,282,844 | 256.009 MB | N/A | 30.64 % |
| GroupBySkipAny | 603.112 ms | 581.099 ms | 2,054,976,446 | 256.009 MB | N/A | 30.31 % |
| HashSet | 865.449 ms | 854.386 ms | 2,949,024,388 | 8.000 KB | Base | 0.00 % |
--- Scale 100,000,000 --------------------------------------------------------- Time 38.508 ---
| Dictionary | 4,394.937 ms | 4,261.656 ms | 14,973,292,181 | 8.000 KB | N/A | 50.11 % |
| GroupBySkipAny | 5,799.055 ms | 5,718.249 ms | 19,758,314,574 | 2.000 GB | N/A | 34.16 % |
| GroupByCount | 5,909.234 ms | 5,781.676 ms | 20,126,526,198 | 2.000 GB | N/A | 32.91 % |
| HashSet | 8,808.441 ms | 8,617.298 ms | 30,010,947,763 | 8.000 KB | Base | 0.00 % |
-----------------------------------------------------------------------------------------------
算法是
词典
public class Dictionary : Benchmark<List<string>, List<string>>
{
public static IEnumerable<string> GetDistinctDuplicates(IEnumerable<string> original)
{
var dict = new Dictionary<string, bool>();
foreach (var s in original)
if (dict.TryGetValue(s, out var isReturnedDupl))
{
if (isReturnedDupl)
continue;
dict[s] = true;
yield return s;
}
else
dict.Add(s, false);
}
protected override List<string> InternalRun()
{
return GetDistinctDuplicates(Input).ToList();
}
}
GroupByCount
public class GroupBy : Benchmark<List<string>, List<string>>
{
protected override List<string> InternalRun()
{
return Input.GroupBy(x => x)
.Where(g => g.Count() > 1)
.Select(y => y.Key)
.ToList();
}
}
GroupBySkipAny Enigmativity
public class GroupBy2 : Benchmark<List<string>, List<string>>
{
protected override List<string> InternalRun()
{
return Input.GroupBy(x => x)
.Where(g => g.Count() > 1)
.Select(y => y.Key)
.ToList();
}
}
摘要
Dictionary是最快的，GroupBy始终表现良好， Enigmativitys 版本Skip和Any略快，并且由于某种原因Hashset总是慢约35-50％。然而，在较小的尺度上，事情并不那么确定。显示结果，甚至是周期和给出的测试数据似乎很清楚，虽然我有一种感觉，因为其他答案基准测试得到的结果不同，可能会有更多的发挥作用。
无论如何都很有趣找到重复
答案 1 :(得分：5)
没有linq，纯粹的代码
获取所有重复
public static IEnumerable<string> GetDuplicates(IEnumerable<string> original)
{
var hs = new HashSet<string>();
foreach (var item in original)
{
if (!hs.Add(item))
{
yield return item;
}
}
}
获取不同的重复
public static IEnumerable<string> GetDistinctDuplicates(IEnumerable<string> original)
{
var dict = new Dictionary<string, bool>();
foreach (var s in original)
{
// If found duplicate
if (dict.TryGetValue(s, out var isReturnedDupl))
{
// If already returned
if (isReturnedDupl)
{
continue;
}
dict[s] = true;
yield return s;
}
else
{
// First meet
dict.Add(s, false);
}
}
}
更新：添加工作台
Update2 ：更新替补席源，替补结果
Update3 ：将MemoryDiagnoser添加到工作台和其他算法
TheGeneral替补与我的差距
| TheGeneral | My bench |
---------- |-------------------- |----------------------- |
Used tool | Own benchmark lib | BenchmarkDotNet |
Input | Random string cases | Corner cases |
算法
- HashSet（GetDuplicates）
- Dict（GetDistinctDuplicates）
- GroupBy（TheGeneral方法）
- GroupByWithSkip（Enigmativity方法）
使用默认配置
对BenchmarkDotNet进行基准测试输入
- AllDupl - 当集合仅包含相同的字符串 时的极端情况
- NoDupl - 当集合仅包含uniq字符串时的极端情况
的Ini ：
BenchmarkDotNet=v0.10.14, OS=Windows 10.0.17134
Intel Core i7-4710HQ CPU 2.50GHz (Haswell), 1 CPU, 8 logical and 4 physical cores
[Host] : .NET Framework 4.6.2 (CLR 4.0.30319.42000), 32bit LegacyJIT-v4.7.3101.0
DefaultJob : .NET Framework 4.6.2 (CLR 4.0.30319.42000), 32bit LegacyJIT-v4.7.3101.0
图例
input : Value of the 'input' parameter
description : Value of the 'description' parameter
Mean : Arithmetic mean of all measurements
Error : Half of 99.9% confidence interval
StdDev : Standard deviation of all measurements
Gen 0 : GC Generation 0 collects per 1k Operations
Gen 1 : GC Generation 1 collects per 1k Operations
Gen 2 : GC Generation 2 collects per 1k Operations
Allocated : Allocated memory per single operation (managed only, inclusive, 1KB = 1024B)
1 us : 1 Microsecond (0.000001 sec)
结果
Method | input | description | Mean | Error | StdDev | Gen 0 | Gen 1 | Gen 2 | Allocated |
---------------- |-------------- |-------------------------- |-------------:|------------:|------------:|----------:|----------:|---------:|-----------:|
--------------------------------------------------------------------------------------------------------------------------------------------------------
GroupBy | Array[1000] | AllDupl, Count=1000 | 43.62 us | 0.6882 us | 0.5747 us | 2.6855 | - | - | 8606 B |
GroupByWithSkip | Array[1000] | AllDupl, Count=1000 | 42.86 us | 0.3188 us | 0.2826 us | 2.7466 | - | - | 8669 B |
HashSet | Array[1000] | AllDupl, Count=1000 | 72.54 us | 0.3339 us | 0.3124 us | 0.1221 | - | - | 429 B |
Dict | Array[1000] | AllDupl, Count=1000 | 35.44 us | 0.1953 us | 0.1731 us | 0.0610 | - | - | 244 B |
GroupBy | Array[1000] | NoDupl, Count=1000 | 110.13 us | 0.2874 us | 0.2548 us | 17.8223 | - | - | 56408 B |
GroupByWithSkip | Array[1000] | NoDupl, Count=1000 | 153.37 us | 0.6419 us | 0.5690 us | 38.0859 | - | - | 120411 B |
HashSet | Array[1000] | NoDupl, Count=1000 | 49.50 us | 0.1833 us | 0.1715 us | 18.4937 | - | - | 58672 B |
Dict | Array[1000] | NoDupl, Count=1000 | 71.20 us | 0.1944 us | 0.1723 us | 23.0713 | - | - | 73027 B |
--------------------------------------------------------------------------------------------------------------------------------------------------------
GroupBy | Array[10000] | AllDupl, Count=10000 | 431.36 us | 1.8869 us | 1.7650 us | 41.5039 | - | - | 131580 B |
GroupByWithSkip | Array[10000] | AllDupl, Count=10000 | 431.19 us | 1.3593 us | 1.2050 us | 41.5039 | - | - | 131680 B |
HashSet | Array[10000] | AllDupl, Count=10000 | 721.68 us | 2.0894 us | 1.7448 us | - | - | - | 432 B |
Dict | Array[10000] | AllDupl, Count=10000 | 357.74 us | 1.3790 us | 1.2899 us | - | - | - | 248 B |
GroupBy | Array[10000] | NoDupl, Count=10000 | 1,316.20 us | 8.2301 us | 7.6984 us | 119.1406 | 29.2969 | - | 611337 B |
GroupByWithSkip | Array[10000] | NoDupl, Count=10000 | 1,908.77 us | 15.7756 us | 14.7565 us | 203.1250 | 97.6563 | - | 1251339 B |
HashSet | Array[10000] | NoDupl, Count=10000 | 696.26 us | 0.9738 us | 0.6441 us | 94.7266 | 94.7266 | 94.7266 | 538736 B |
Dict | Array[10000] | NoDupl, Count=10000 | 954.53 us | 1.9645 us | 1.8376 us | 124.0234 | 124.0234 | 124.0234 | 673164 B |
--------------------------------------------------------------------------------------------------------------------------------------------------------
GroupBy | Array[100000] | AllDupl, Count=100000 | 4,767.00 us | 17.4749 us | 16.3461 us | 281.2500 | 281.2500 | 281.2500 | 1051088 B |
GroupByWithSkip | Array[100000] | AllDupl, Count=100000 | 4,742.72 us | 22.8393 us | 21.3639 us | 281.2500 | 281.2500 | 281.2500 | 1051088 B |
HashSet | Array[100000] | AllDupl, Count=100000 | 7,247.34 us | 12.4036 us | 11.6023 us | - | - | - | 448 B |
Dict | Array[100000] | AllDupl, Count=100000 | 3,557.70 us | 14.2987 us | 11.1635 us | - | - | - | 256 B |
GroupBy | Array[100000] | NoDupl, Count=100000 | 31,044.51 us | 371.9730 us | 347.9438 us | 1125.0000 | 750.0000 | 312.5000 | 5849142 B |
GroupByWithSkip | Array[100000] | NoDupl, Count=100000 | 42,374.47 us | 306.7762 us | 286.9586 us | 2187.5000 | 1187.5000 | 500.0000 | 12249704 B |
HashSet | Array[100000] | NoDupl, Count=100000 | 7,497.73 us | 54.6210 us | 51.0925 us | 656.2500 | 593.7500 | 593.7500 | 4830548 B |
Dict | Array[100000] | NoDupl, Count=100000 | 9,825.25 us | 51.1668 us | 45.3581 us | 1062.5000 | 984.3750 | 984.3750 | 6042773 B |
<强>摘要
GroupBy ， HashSet 和 Dict 的性能在很大程度上取决于输入。如果输入仅包含重复项 - Dictionary 更好。但是当输入只包含uniq值 - HashSet 时更好。使用随机输入（如在通用代码中） GroupBy 比 HashSet 效果更好。另请注意，仅使用uniq值的输入 - 对于具有巨大性能命中的 GroupBy 来说确实是最糟糕的情况。 分配和GC真的很有趣的结果......
因此，更重要的是取决于输入重复次数，输入总数和目标
来源
class Program
{
static void Main(string[] args)
{
var conf = ManualConfig.Create(DefaultConfig.Instance);
conf.Add(MemoryDiagnoser.Default);
var summary = BenchmarkRunner.Run<DuplicateFindBench>(conf);
}
}
public class DuplicateFindBench
{
[Benchmark]
[ArgumentsSource(nameof(Data))]
public List<string> GroupBy(string[] input, string description)
{
return input.GroupBy(x => x)
.Where(g => g.Count() > 1)
.Select(y => y.Key)
.ToList();
}
[Benchmark]
[ArgumentsSource(nameof(Data))]
public List<string> GroupByWithSkip(string[] input, string description)
{
return input.GroupBy(x => x)
.Where(g => g.Skip(1).Any())
.Select(y => y.Key)
.ToList();
}
[Benchmark]
[ArgumentsSource(nameof(Data))]
public List<string> HashSet(string[] input, string description)
{
return GetDuplicates(input).Distinct().ToList();
}
[Benchmark]
[ArgumentsSource(nameof(Data))]
public List<string> Dict(string[] input, string description)
{
return GetDistinctDuplicates(input).ToList();
}
public static IEnumerable<string> GetDuplicates(IEnumerable<string> original)
{
var hs = new HashSet<string>();
foreach (var item in original)
{
if (!hs.Add(item))
{
yield return item;
}
}
}
public static IEnumerable<string> GetDistinctDuplicates(IEnumerable<string> original)
{
var dict = new Dictionary<string, bool>();
foreach (var s in original)
{
// If found duplicate
if (dict.TryGetValue(s, out var isReturnedDupl))
{
// If already returned
if (isReturnedDupl)
{
continue;
}
dict[s] = true;
yield return s;
}
else
{
// First meet
dict.Add(s, false);
}
}
}
public IEnumerable<object[]> Data()
{
const int count1 = 1000;
yield return new object[] { ArrayParam<string>.ForPrimitives(CreateNoDuplInput(count1).ToArray()), $"NoDupl, Count={count1}" };
yield return new object[] { ArrayParam<string>.ForPrimitives(CreateAllDuplInput(count1).ToArray()), $"AllDupl, Count={count1}" };
const int count2 = 10_000;
yield return new object[] { ArrayParam<string>.ForPrimitives(CreateNoDuplInput(count2).ToArray()), $"NoDupl, Count={count2}" };
yield return new object[] { ArrayParam<string>.ForPrimitives(CreateAllDuplInput(count2).ToArray()), $"AllDupl, Count={count2}" };
const int count3 = 100_000;
yield return new object[] { ArrayParam<string>.ForPrimitives(CreateNoDuplInput(count3).ToArray()), $"NoDupl, Count={count3}" };
yield return new object[] { ArrayParam<string>.ForPrimitives(CreateAllDuplInput(count3).ToArray()), $"AllDupl, Count={count3}" };
}
public List<string> CreateNoDuplInput(int inputSize)
{
var result = new List<string>();
for (int i = 0; i < inputSize; i++)
{
result.Add(i.ToString());
}
return result;
}
public List<string> CreateAllDuplInput(int inputSize)
{
var result = new List<string>();
for (int i = 0; i < inputSize; i++)
{
result.Add("duplicate value");
}
return result;
}
}
答案 2 :(得分：2)
在linq或SQL中，您必须使用EXCEPT代替减号，如下所示：
var namesCollisions = test.Except(test.Distinct().ToList());
但是我无法理解你想要的结果，这个答案总是返回空列表。
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