From 0602352705ae45e897c42bf7380143d1fa7f2472 Mon Sep 17 00:00:00 2001
From: Christoph Ruegg <git@cdrnet.ch>
Date: Sun, 11 Feb 2018 09:11:49 +0100
Subject: [PATCH] BREAKING: Statistics: Ranks and RankInplace of single
 precision to return single precision arrays #364

---
 .../Statistics/ArrayStatistics.Single.cs      | 38 ++++++++++++++++++-
 src/Numerics/Statistics/Statistics.cs         |  2 +-
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/src/Numerics/Statistics/ArrayStatistics.Single.cs b/src/Numerics/Statistics/ArrayStatistics.Single.cs
index 7614cf12..9cba31de 100644
--- a/src/Numerics/Statistics/ArrayStatistics.Single.cs
+++ b/src/Numerics/Statistics/ArrayStatistics.Single.cs
@@ -759,9 +759,9 @@ namespace MathNet.Numerics.Statistics
         /// with an existing system.
         /// WARNING: Works inplace and can thus causes the data array to be reordered.
         /// </summary>
-        public static double[] RanksInplace(float[] data, RankDefinition definition = RankDefinition.Default)
+        public static float[] RanksInplace(float[] data, RankDefinition definition = RankDefinition.Default)
         {
-            var ranks = new double[data.Length];
+            var ranks = new float[data.Length];
             var index = new int[data.Length];
             for (int i = 0; i < index.Length; i++)
             {
@@ -803,5 +803,39 @@ namespace MathNet.Numerics.Statistics
             RanksTies(ranks, index, previousIndex, data.Length, definition);
             return ranks;
         }
+
+        static void RanksTies(float[] ranks, int[] index, int a, int b, RankDefinition definition)
+        {
+            // TODO: potential for PERF optimization
+            float rank;
+            switch (definition)
+            {
+                case RankDefinition.Average:
+                {
+                    rank = (b + a - 1) / 2f + 1;
+                    break;
+                }
+
+                case RankDefinition.Min:
+                {
+                    rank = a + 1;
+                    break;
+                }
+
+                case RankDefinition.Max:
+                {
+                    rank = b;
+                    break;
+                }
+
+                default:
+                    throw new NotSupportedException();
+            }
+
+            for (int k = a; k < b; k++)
+            {
+                ranks[index[k]] = rank;
+            }
+        }
     }
 }
diff --git a/src/Numerics/Statistics/Statistics.cs b/src/Numerics/Statistics/Statistics.cs
index b1c887f9..04a04ca1 100644
--- a/src/Numerics/Statistics/Statistics.cs
+++ b/src/Numerics/Statistics/Statistics.cs
@@ -1267,7 +1267,7 @@ namespace MathNet.Numerics.Statistics
         /// </summary>
         /// <param name="data">The data sample sequence.</param>
         /// <param name="definition">Rank definition, to choose how ties should be handled and what product/definition it should be consistent with</param>
-        public static double[] Ranks(this IEnumerable<float> data, RankDefinition definition = RankDefinition.Default)
+        public static float[] Ranks(this IEnumerable<float> data, RankDefinition definition = RankDefinition.Default)
         {
             float[] array = data.ToArray();
             return ArrayStatistics.RanksInplace(array, definition);