AK: Add Statistics helper

This patch adds a helper to AK which allows for basic statistical
analysis of values.
The median algorithm is very naive and slow, but it works.

AK/Statistics.h

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2021, Tobias Christiansen <tobyase@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Math.h>
+#include <AK/QuickSort.h>
+#include <AK/StdLibExtraDetails.h>
+#include <AK/Vector.h>
+
+namespace AK {
+
+template<typename T = float>
+requires(IsArithmetic<T>) class Statistics {
+public:
+    Statistics() = default;
+    ~Statistics() = default;
+
+    void add(T const& value)
+    {
+        // FIXME: Check for an overflow
+        m_sum += value;
+        m_values.append(value);
+    }
+
+    T const sum() const { return m_sum; }
+    float average() const { return (float)sum() / size(); }
+
+    // FIXME: Implement a better algorithm
+    T const median()
+    {
+        quick_sort(m_values);
+        return m_values.at(size() / 2);
+    }
+
+    float standard_deviation() const { return sqrt(variance()); }
+    float variance() const
+    {
+        float summation = 0;
+        float avg = average();
+        for (T number : values()) {
+            float difference = (float)number - avg;
+            summation += (difference * difference);
+        }
+        summation = summation / size();
+        return summation;
+    }
+
+    Vector<T> const& values() const { return m_values; }
+    size_t size() const { return m_values.size(); }
+
+private:
+    Vector<T> m_values;
+    T m_sum {};
+};
+
+}