add list extension to calc median

vis3d/unity/Assets/_app/Scripts/EnumerableEx.cs

+using System;
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+
+public static class EnumerableEx
+{
+  static int[] indices = new int[1024];
+
+  //https://github.com/jianminchen/AlgorithmsPractice/blob/master/quickSortAlgorithm.cs
+  //left and right are inclusive
+  private static void Quick_Sort_indices<T>(IEnumerable<T> that, int[] indices, int left, int right, Func<T, T, int> comparer)
+  {
+    if (left > right || left < 0 || right < 0) return;
+
+    int index = partition(that, indices, left, right, comparer);
+
+    if (index != -1)
+    {
+      Quick_Sort_indices(that, indices, left, index - 1, comparer);
+      Quick_Sort_indices(that, indices, index + 1, right, comparer);
+    }
+  }
+
+  private static int partition<T>(IEnumerable<T> that, int[] indices, int left, int right, Func<T, T, int> comparer)
+  {
+    if (left > right) return -1;
+
+    int end = left;
+
+    T pivot = GetElement(that, indices, right);    // choose last one to pivot, easy to code
+    for (int i = left; i < right; i++)
+    {
+      if (comparer( GetElement(that, indices,i), pivot) < 0)
+      {
+        swap(indices, i, end);
+        end++;
+      }
+    }
+
+    swap(indices, end, right);
+
+    return end;
+  }
+
+  private static void swap(int[] A, int left, int right)
+  {
+    int tmp = A[left];
+    A[left] = A[right];
+    A[right] = tmp;
+  }
+
+  private static T GetElement<T>(IEnumerable<T> enumerable, int[] indices, int index)
+  {
+    var array = enumerable as T[];
+    if (array != null)
+    {
+      return array[indices[index]];
+    }
+
+    var list = enumerable as List<T>;
+    if (list != null)
+    {
+      return list[indices[index]];
+    }
+
+    int i = 0;
+    foreach (var item in enumerable)
+    {
+      if (i == index) return item;
+      ++i;
+    }
+
+    throw new ArgumentOutOfRangeException("index");
+  }
+
+  private static int SortIndices<T>(IEnumerable<T> that, Func<T, T, int> comparer)
+  {
+    int n = Count(that);
+
+    if (indices.Length < n)
+    {
+      indices = new int[indices.Length + n];
+    }
+
+    for (int i = 0; i != n; ++i)
+    {
+      indices[i] = i;
+    }
+
+    Quick_Sort_indices<T>(that, indices, 0, n-1, comparer);
+    return n;
+  }
+
+  public static int MedianIndex<T>(this IEnumerable<T> that, Func<T, T, int> comparer)
+  {
+    int n = SortIndices(that, comparer);
+
+    return indices[n / 2];
+  }
+
+  public static int MinIndex<T>(this IEnumerable<T> that, Func<T, T, int> comparer)
+  {
+    SortIndices(that, comparer);
+
+    return indices[0];
+  }
+
+  public static int MaxIndex<T>(this IEnumerable<T> that, Func<T, T, int> comparer)
+  {
+    int n = SortIndices(that, comparer);
+
+    return indices[n - 1];
+  }
+
+  private static int Count<T>(IEnumerable<T> enumerable)
+  {
+    var array = enumerable as T[];
+    if (array != null)
+    {
+      return array.Length;
+    }
+
+    var list = enumerable as List<T>;
+    if (list != null)
+    {
+      return list.Count;
+    }
+
+    int n = 0;
+    foreach (var item in enumerable)
+    {
+      ++n;
+    }
+
+    return n;
+  }
+}

vis3d/unity/Assets/_app/Scripts/EnumerableEx.cs.meta

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