以特定顺序比较器对列表进行排序

Question

我有一个字符串列表，我需要编写一个 IComparer 实现来按特定顺序对它们进行排序。

我当前的实现：

public enum TimeBucket
{
    [Description("0D")]
    ZeroDay,
    [Description("1D")]
    OneDay,
    [Description("1W")]
    OneWeek,
    [Description("2W")]
    TwoWeek,
    [Description("0M")]
    ZeroMonth,
    [Description("1M")]
    OneMonth
}

public class TimeBucketComparer : IComparer
{
    public static TimeBucketComparer Instance { get; } = new TimeBucketComparer();

    private TimeBucketComparer()
    {

    }

    public int Compare(object x, object y)
    {
        TimeBucket xvar = GetValue(string.Join("", x.ToString().Split(' ')));
        TimeBucket yvar = GetValue(string.Join("", y.ToString().Split(' ')));

        if (EqualityComparer<TimeBucket>.Default.Equals(xvar, default(TimeBucket)) &&
            EqualityComparer<TimeBucket>.Default.Equals(yvar, default(TimeBucket)))
            return String.CompareOrdinal(xvar.ToString(), yvar.ToString());

        if (EqualityComparer<TimeBucket>.Default.Equals(xvar, default(TimeBucket))) return -1;
        if (EqualityComparer<TimeBucket>.Default.Equals(yvar, default(TimeBucket))) return 1;

        return xvar.CompareTo(yvar);
    }

    public TimeBucket GetValue(string description) => EnumExtensions.GetValueFromDescription<TimeBucket>(description);


}
public static class EnumExtensions
{
    public static string GetDescription(this Enum value)
    {
        return ((DescriptionAttribute)Attribute.GetCustomAttribute(value.GetType().GetFields(BindingFlags.Public | BindingFlags.Static).Single(x => x.GetValue(null).Equals(value)),typeof(DescriptionAttribute)))?.Description ?? value.ToString();
    }

    public static T GetValueFromDescription<T>(string description)
    {
        var type = typeof(T);
        if (!type.IsEnum) throw new InvalidOperationException();
        foreach (var field in type.GetFields())
        {
            var attribute = Attribute.GetCustomAttribute(field,
                typeof(DescriptionAttribute)) as DescriptionAttribute;
            if (attribute != null)
            {
                if (attribute.Description == description)
                    return (T)field.GetValue(null);
            }
            else
            {
                if (field.Name == description)
                    return (T)field.GetValue(null);
            }
        }
        throw new ArgumentException("Not found.", "description");
        // or return default(T);
    }
}

由于涉及反射，我当前的实现需要花费大量时间。我使用这种方式是因为需要一个通用的实现。输入至少有 40000 条需要排序的 Timebuckets 记录。排序算法是 linq orderby，它是通用的，不能修改。因此，需要使用比较器。

我需要对字符串进行排序。有没有更好的不使用反射的方法？

编辑：如果不清楚，我的输入是 {"1M", "1D", "1W", "0D"} 我需要的输出是 {"0D", "1D", "1W ", "1M"}

Answer 1

像这样定义枚举：

public enum TimeBucket
    {
        [Description("0D")]
        ZeroDay = 0,
        [Description("1D")]
        OneDay = 1,
        [Description("1W")]
        OneWeek = 2,
        [Description("2W")]
        TwoWeek = 3,
        [Description("0M")]
        ZeroMonth = 4,
        [Description("1M")]
        OneMonth = 5
    }

假设此枚举是某个实体的属性，并且您想对该实体的集合进行排序。

例如：

var sortedList = coll.OrderBy(x => (int) (x.TimeBucket)).ToList();

Answer 2

我没有得到你的排序逻辑，但无论如何 - 如果你因为反射而遇到性能问题 - 只需进行一次反射并缓存结果。例如：

public class TimeBucketComparer : IComparer, IComparer<string> {
    public static TimeBucketComparer Instance { get; } = new TimeBucketComparer();

    private static readonly Lazy<Dictionary<string, TimeBucket>> _values = new Lazy<Dictionary<string, TimeBucket>>(() => {
        // get all fields and store in dictionary, keyed by description attribute
        return typeof(TimeBucket)
            .GetFields(BindingFlags.Public | BindingFlags.Static)
            .ToDictionary(c => 
                c.GetCustomAttribute<DescriptionAttribute>()?.Description ?? c.Name, 
                c => (TimeBucket) c.GetValue(null));
    });

    private TimeBucketComparer() {

    }

    public int Compare(object x, object y) {
        string xvar = string.Join("", x.ToString().Split(' '));
        string yvar = string.Join("", y.ToString().Split(' '));
        return Compare(xvar, yvar);   
    }

    public int Compare(string x, string y) {
        if (!_values.Value.ContainsKey(x))
        {
            // do something, invalid value
            throw new ArgumentException(nameof(x));
        }
        if (!_values.Value.ContainsKey(y))
        {
            // do something, invalid value
            throw new ArgumentException(nameof(y));
        }
        return _values.Value[x].CompareTo(_values.Value[y]);
    }
}

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