From a761d0e8f2286b832345147fbd545c6e687615a6 Mon Sep 17 00:00:00 2001
From: Arkadiusz Kondas <arkadiusz.kondas@gmail.com>
Date: Sun, 8 May 2016 19:23:54 +0200
Subject: [PATCH] mode (dominant) from numbers

---
 src/Phpml/Math/Statistic/Mean.php       | 39 ++++++++++++++++++++++---
 tests/Phpml/Math/Statistic/MeanTest.php | 26 ++++++++++++++++-
 2 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/src/Phpml/Math/Statistic/Mean.php b/src/Phpml/Math/Statistic/Mean.php
index 0988e01..9d87a97 100644
--- a/src/Phpml/Math/Statistic/Mean.php
+++ b/src/Phpml/Math/Statistic/Mean.php
@@ -12,9 +12,13 @@ class Mean
      * @param array $numbers
      *
      * @return float
+     *
+     * @throws InvalidArgumentException
      */
     public static function arithmetic(array $numbers)
     {
+        self::checkArrayLength($numbers);
+
         return array_sum($numbers) / count($numbers);
     }
 
@@ -26,11 +30,10 @@ class Mean
      * @throws InvalidArgumentException
      */
     public static function median(array $numbers) {
-        $count = count($numbers);
-        if (0 == $count) {
-            throw InvalidArgumentException::arrayCantBeEmpty();
-        }
 
+        self::checkArrayLength($numbers);
+
+        $count = count($numbers);
         $middleIndex = floor($count / 2);
         sort($numbers, SORT_NUMERIC);
         $median = $numbers[$middleIndex];
@@ -42,4 +45,32 @@ class Mean
         return $median;
     }
 
+    /**
+     * @param array $numbers
+     *
+     * @return mixed
+     *
+     * @throws InvalidArgumentException
+     */
+    public static function mode(array $numbers)
+    {
+        self::checkArrayLength($numbers);
+
+        $values = array_count_values($numbers);
+
+        return array_search(max($values), $values);
+    }
+
+    /**
+     * @param array $array
+     *
+     * @throws InvalidArgumentException
+     */
+    private static function checkArrayLength(array $array)
+    {
+        if (0 == count($array)) {
+            throw InvalidArgumentException::arrayCantBeEmpty();
+        }
+    }
+
 }
diff --git a/tests/Phpml/Math/Statistic/MeanTest.php b/tests/Phpml/Math/Statistic/MeanTest.php
index d56f965..289f9a3 100644
--- a/tests/Phpml/Math/Statistic/MeanTest.php
+++ b/tests/Phpml/Math/Statistic/MeanTest.php
@@ -8,6 +8,15 @@ use Phpml\Math\Statistic\Mean;
 
 class MeanTest extends \PHPUnit_Framework_TestCase
 {
+
+    /**
+     * @expectedException \Phpml\Exception\InvalidArgumentException
+     */
+    public function testArithmeticThrowExceptionOnEmptyArray()
+    {
+        Mean::arithmetic([]);
+    }
+
     public function testArithmeticMean()
     {
         $delta = 0.01;
@@ -19,7 +28,7 @@ class MeanTest extends \PHPUnit_Framework_TestCase
     /**
      * @expectedException \Phpml\Exception\InvalidArgumentException
      */
-    public function testThrowExceptionOnEmptyArrayMedian()
+    public function testMedianThrowExceptionOnEmptyArray()
     {
         Mean::median([]);
     }
@@ -38,4 +47,19 @@ class MeanTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals(3.5, Mean::median($numbers));
     }
 
+    /**
+     * @expectedException \Phpml\Exception\InvalidArgumentException
+     */
+    public function testModeThrowExceptionOnEmptyArray()
+    {
+        Mean::mode([]);
+    }
+
+    public function testModeOnArray()
+    {
+        $numbers = [5, 2, 6, 1, 3, 4, 6, 6, 5];
+
+        $this->assertEquals(6, Mean::mode($numbers));
+    }
+
 }