我需要将两个非常大的集合与可能缺少的元素进行比较

Question

我在为我的工作写的一个程序中遇到了一堵砖墙.你不需要特别了解上下文,但长话短说,我有两个大约约650k记录的集合.

我们假设集合A是我认识的正确的集合,集合B是我知道的不正确的集合.

集合B包含一个复杂的对象,它具有与集合A中的元素相同类型的属性(换句话说,它看起来有点像这样):

// Where T : IComparable
IEnumerable<DateTime> A = ...; // Collection of T elements
IEnumerable<Complex> B = ...; // Collection of complex elements.
class Complex<DateTime>
{
   public DateTime Time { get; set; }
   .....
}

我的问题是我基本上需要按顺序枚举A并查看A的当前元素是否存在于B中的Complex对象中; 如果它不存在,那么我需要创建一个Complex对象,它将封装该元素(以及其他内容).

当我意识到这两个列表长度为650,000个元素时,会出现问题.我无法减少数据集; 我必须使用这些650,000.现在我已经使用了ICollection.Contains(),我尝试了(天真)二进制搜索的实现,但它只需要太长时间.

你有什么建议吗？

编辑:如果有帮助,T实现IComparable.EDIT2:更多上下文:使用Linq To Objects从DataTable中检索IEnumerable.

        IEnumerable<Complex> set = set.Tbl
            .Where(dbObject => dbObject.TS.CompareTo(default(DateTime)) != 0)
            .Select(Func<DataRow,Complex>) // Function that wraps the DataRow in a Complex object
            // Just done to make debugging a little easier so we still have a large sample but small enough that it doesn't make me grow a beard
            .Take(100000) 
            .AsEnumerable<Complex>();

为了完整性,如果这个问题被存档并且其他任何人需要解决这个问题,我当前的实现看起来有点像这样

        BDataSet bSet = new BDataSet();
        B_LUTableAdapter adap = new B_LUTableAdapter();
        adap.Fill(bSet.B_LU);
        IEnumerable<Complex> w3 = bSet.B
            .Where(dbObject => dbObject.TS.CompareTo(default(DateTime)) != 0)
            // Function that just wraps datarow into a complex object
            .Select(Func<DataRow, Complex>)
            // Just for sake of debugging speed
            .Take(100000)
            .AsEnumerable<Complex>();

        List<Complex> b = bSet.OrderBy(x => x.Time).ToList<Complex>();
        // Get last & first timestamps
        // Some of the timestamps in b are 01/01/1011 for some reason,
        // So we do this check.
        Complex start = b.Where(x => x.Time != default(DateTime)).First();
        Complex end = b.Last();

        List<DateTime> a = new List<DateTime>();
        // RoundSeconds reduces seconds in a DateTime to 0.
        DateTime current = RoundSeconds(new DateTime(start.Time.Ticks));

        while (current.CompareTo(RoundSeconds(end.Time)) <= 0)
        {
            a.Add(current);
            current = current.Add(TimeSpan.FromMinutes(1));
        }

        IEnumerable<DateTime> times = b.Select(x => x.Time);
        var missing = a.Where(dt => times.Contains(dt));
        foreach (var dt in missing)
        {
            adap.Insert(dt, 0, "", "", "", null, 0, 0);
            // This has since been changed to List.Add()
        }

感谢Cosmin,此问题现已解决,完成的实现是:List expected = new List(); DateTime current = RoundSeconds(new DateTime(start.Time.Ticks));

        while (current.CompareTo(RoundSeconds(end.Time)) <= 0)
        {
            expected.Add(current);
            current = current.Add(TimeSpan.FromMinutes(1));
        }

        Console.WriteLine("Expecting {0} intervals.", expected.Count);
        var missing = b.FindAllMissing(expected, x => x.Time);
        if(!missing.Any()) return;
        Console.WriteLine("{0} missing intervals.", missing.Count());
        foreach (var dt in missing)
        {
            b.Add(new Complex() { /* some values */ });
            //Console.WriteLine("\t> Inserted new record at {0}", dt);
        }

        //.....
        public static IEnumerable<Basic> FindAllMissing<Basic, Complex>(this IEnumerable<Complex> complexList,
        IEnumerable<Basic> basicList,
        Func<Complex, Basic> selector)
        {
            HashSet<Basic> inComplexList = new HashSet<Basic>();
            foreach (Complex c in complexList)
                inComplexList.Add(selector(c));
            List<Basic> missing = new List<Basic>();
            foreach (Basic basic in basicList)
                if (!(inComplexList.Contains(basic)))
                    missing.Add(basic);
            return missing;
        }

Answer 1

一步步：

• 使用通用集合之一O(1)创建T第二个集合中已存在的可快速搜索的列表。我可以建议吗HashSet<T>
• 枚举 SECOND 集合并将T第一步中的所有 ' 放入集合中。
• 枚举第一个集合并检查每个项目是否位于第一步创建的集合中。既然该操作O(1)现在已经有了O(n)解决方案。
• 享受。

下面是一个将该算法实现为通用扩展方法的类，以使其更加 LINQ 友好。使其参数为IEnumerable<T>和 return IEnumerable<T>，对类型 (T和Complex) 没有做出任何假设。在我的测试中，我使用一个列表Tuple<int,int>作为复杂类型，使用一个简单列表int作为简单类型。控制台应用程序List<Tuple<int,int>>用 600000 个值填充 ，然后将 100000 个值放入 simple 中List<int>，使用枚举器来计算 ; 中未找到的所有简单值List<Tuple<int,int>>。它太快了，你没有机会看到它正在工作，当你点击F5它时，只会显示结果。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication2
{

    static class FixProblem
    {
        public static IEnumerable<T> FindAllThatNeedCreating<T, Complex>(this IEnumerable<Complex> list_of_complex, IEnumerable<T> list_of_T, Func<Complex, T> extract)
        {
            HashSet<T> T_in_list_of_complex = new HashSet<T>();
            foreach (Complex c in list_of_complex)
                T_in_list_of_complex.Add(extract(c));
            List<T> answer = new List<T>();
            foreach (T t in list_of_T)
                if (!T_in_list_of_complex.Contains(t))
                    answer.Add(t);
            return answer;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            // Test the code
            List<Tuple<int, int>> complex = new List<Tuple<int, int>>();
            List<int> simple = new List<int>();

            // Fill in some random data
            Random rnd = new Random();
            for (int i = 1; i < 600000; i++)
                complex.Add(new Tuple<int, int>(rnd.Next(), rnd.Next()));

            for (int i = 1; i < 100000; i++)
                simple.Add(rnd.Next());

            // This is the magic line of code:
            Console.WriteLine(complex.FindAllThatNeedCreating(simple, x => x.Item1).Count());

            Console.ReadKey();

        }
    }
}