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  1. using System;
  2. using System.Collections;
  3. using System.Collections.Generic;
  4. using System.Linq;
  5. using System.Text;
  6.  
  7. namespace GroupByCluster
  8. {
  9.     public static class EnumerableExtensions
  10.     {
  11.         class ClusterGrouping<T> : IGrouping<T, T>
  12.         {
  13.             public T Key { get; private set; }
  14.  
  15.             public IEnumerator<T> GetEnumerator()
  16.             {
  17.                 return items.GetEnumerator();
  18.             }
  19.  
  20.             IEnumerator IEnumerable.GetEnumerator()
  21.             {
  22.                 return GetEnumerator();
  23.             }
  24.  
  25.             internal readonly List<T> items = new List<T>();
  26.  
  27.             internal ClusterGrouping(T t)
  28.             {
  29.                 Key = t;
  30.                 items.Add(t);
  31.             }
  32.  
  33.             internal ClusterGrouping(IEnumerable<ClusterGrouping<T>> containingGroups)
  34.             {
  35.                 Key = containingGroups.First().Key;
  36.                 items.AddRange(containingGroups.SelectMany(g => g));
  37.             }
  38.  
  39.             internal void Include(T t)
  40.             {
  41.                 items.Add(t);
  42.             }
  43.         }
  44.  
  45.         public static IEnumerable<IGrouping<T, T>> GroupByCluster<T>(this IEnumerable<T> source, Func<T, T, double> distance, double eps)
  46.         {
  47.             var result = new HashSet<ClusterGrouping<T>>();
  48.             foreach (T t in source)
  49.             {
  50.                 // need to materialize, as we are changing the result
  51.                 var containingGroups = result.Where(g => g.Any(gt => distance(t, gt) < eps)).ToList();
  52.                 switch (containingGroups.Count)
  53.                 {
  54.                 case 0:
  55.                     result.Add(new ClusterGrouping<T>(t));
  56.                     break;
  57.                 case 1:
  58.                     containingGroups[0].Include(t);
  59.                     break;
  60.                 default:
  61.                     result.Add(new ClusterGrouping<T>(containingGroups));
  62.                     foreach (var g in containingGroups)
  63.                         result.Remove(g);
  64.                     break;
  65.                 }
  66.             }
  67.             return result;
  68.         }
  69.     }
  70. }
Compilation error #stdin compilation error #stdout 0s 0KB
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stdin
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Standard input is empty
compilation info 
prog.cs(67,13): error CS0266: Cannot implicitly convert type `System.Collections.Generic.HashSet<GroupByCluster.EnumerableExtensions.ClusterGrouping<T>>' to `System.Collections.Generic.IEnumerable<System.Linq.IGrouping<T,T>>'. An explicit conversion exists (are you missing a cast?)
Compilation failed: 1 error(s), 0 warnings
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Standard output is empty
https://ideone.com/8l0LH
language:
C# (gmcs 5.20.1)
created:
11 years ago
visibility:
public

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