c# - 区分忽略空格、变音符号和大小写的字符串列表

Question

给定以下字符串列表:

string[] Itens = new string[] { "hi", " hi   ", "HI", "hí", " Hî", "hi hi", " hí hí ", "olá", "OLÁ", " olá   ", "", "ola", "hola", " holà    ", "aaaa", "áâàa", " aâàa     ", "áaàa", "áâaa ", "aaaa ", "áâaa", "áâaa", };

Distinct 操作的结果应该是:

hi, hi hi, olá, , hola, aaaa

可用于 IEnumerable 的 C# 的 Distinct 操作接受 IEqualityComparer 作为参数，因此我们可以个性化比较。

下面的实现完成了工作

class LengthHash : IEqualityComparer<string>
{
    public bool Equals(string x, string y)
    {
        if (x == null || y == null) return x == y;

        var xt = x.Trim();
        var yt = y.Trim();

        return xt.Length == yt.Length && Culture.CompareInfo.IndexOf(xt, yt, CompareOptions.IgnoreNonSpace | CompareOptions.IgnoreCase) >= 0;
    }

    public int GetHashCode(string obj) => obj?.Trim().Length ?? 1;
}

如果 GetHashCode 不同，Equals 甚至不会执行，因此有一个好的实现很重要。

我尝试将 GetHashCode 更改为其他 2 种不同的方法。

忽略哈希

public int GetHashCode(string obj) => 1;

标准化哈希

public int GetHashCode(string obj) => obj?.Trim().Normalize().ToUpperInvariant().GetHashCode() ?? 1;
// obs: This approach doesn't produce the same output.

除了使用个性化的 IEqualityComparer，我还尝试在执行 StringComparer.InvariantCultureIgnoreCase 之前修剪列表，但它产生与 Normalize 和 Upper 版本相同的输出。

对纯 Distinct、StringComparer.InvariantCultureIgnoreCase 和 3 种个性化方法进行基准测试会产生以下结果:

                              Method |       Mean |    StdErr |    StdDev |     Median |
------------------------------------ |----------- |---------- |---------- |----------- |
                          RunDefault |  2.2224 us | 0.0242 us | 0.2391 us |  2.1414 us |
                     RunHashAsLength |  6.0765 us | 0.0515 us | 0.1857 us |  6.1235 us |
                       RunIgnoreHash |  6.4078 us | 0.0640 us | 0.6140 us |  6.1982 us |
                   RunNormalizedHash | 14.5941 us | 0.0742 us | 0.3556 us | 14.4983 us |
 RunTrimAndCompareWithStringComparer | 14.4935 us | 0.0213 us | 0.0768 us | 14.5352 us |

输出是:

21 Default: hi,  hi   , HI, hí,  Hî, hi hi,  hí hí , olá, OLÁ,  olá   , , ola, hola,  holà    , aaaa, áâàa,  aâàa     , áaàa, áâaa , aaaa , áâaa
6 HashAsLength: hi, hi hi, olá, , hola, aaaa
6 IgnoreHash: hi, hi hi, olá, , hola, aaaa
15 NormalizedHash: hi, hí,  Hî, hi hi,  hí hí , olá, , ola, hola,  holà    , aaaa, áâàa,  aâàa     , áaàa, áâaa
15 RunTrimAndCompareWithStringComparer: hi, hí, Hî, hi hi, hí hí, olá, , ola, hola, holà, aaaa, áâàa, aâàa, áaàa, áâaa

您可以在 https://gist.github.com/Flash3001/d50a6b43bba7bc61e3d85734e40dbed9 中找到完整的测试

问题是:是否有更好的方法来获得所需的最终列表？无论是不同的 GetHashCode、Equals 还是其他预定义的 IEqualityComparer。

Answer 1

您可以使用CompareInfo 类、Compare 和GetHashCode 提供的指定方法。这样您就可以确保实现是一致的。正确性是第一位的。性能是次要的。

class StringEqualityComparer : IEqualityComparer<string>
{
    private CultureInfo _cultureInfo;
    private CompareOptions _options;
    private bool _trim;

    public StringEqualityComparer(CultureInfo cultureInfo,
        CompareOptions options, bool trim)
    {
        _cultureInfo = cultureInfo;
        _options = options;
        _trim = trim;
    }

    public bool Equals(string x, string y)
    {
        if (_trim) { x = x?.Trim(); y = y?.Trim(); }
        return _cultureInfo.CompareInfo.Compare(x, y, _options) == 0;
    }

    public int GetHashCode(string obj)
    {
        if (_trim) obj = obj?.Trim();
        return _cultureInfo.CompareInfo.GetHashCode(obj, _options);
    }
}

使用示例:

var comparer = new StringEqualityComparer(CultureInfo.InvariantCulture,
    CompareOptions.IgnoreNonSpace | CompareOptions.IgnoreCase, true);
var items = new string[] { "hi", " hi   ", "HI", "hí", " Hî", "hi hi", " hí hí ",
    "olá", "OLÁ", " olá   ", "", "ola", "hola", " holà    ", "aaaa", "áâàa",
    " aâàa     ", "áaàa", "áâaa ", "aaaa ", "áâaa", "áâaa", };
Console.WriteLine($"Distinct: {String.Join(", ", items.Distinct(comparer))}");

输出:

Distinct: hi, hi hi, olá, , hola, aaaa