Benford

SE/se-lib/Benford.php

@@ -0,0 +1,78 @@
+<?php
+
+class Benford {
+	private $array = [];
+	private $benford = [];
+
+	public function __construct($array = null) {
+		if ($array !== null) $this->addArray($array);
+	}
+
+	public function addArray($array = null) {
+		if ($array === null) throw new Exception("Missing parameter");
+		if (!is_array($array)) throw new Exception("Bad parameter - non array");
+		foreach ($array as $k => $v) $this->addItem($k, $v);
+	}
+
+	public function addItem($k = null, $v = null) {
+		if (!is_int($k)) throw new Exception("Bad key value - non integer ({$k})");
+		if ($k < 1) throw new Exception("Bad key value - less than 1 ({$k})");
+		if (isset($this->array[$k])) throw new Exception("Key value already exists ({$k})");
+		if (!is_numeric($v)) throw new Exception("Bad value - non numeric ({$v})");
+		$v = round($v * 100);
+		if ($v == 0) return;
+		if ($v < 0) $v *= -1;
+		$this->array[$k] = round($v);
+	}
+
+	private function benford($k = null) {
+		if ($k === null) throw new Exception("Missing parameter");
+		if (!is_int($k)) throw new Exception("Bad parameter - non integer ({$k})");
+		if ($k < 1) throw new Exceptrion("Bad parameter - less than 1 ({$k})");
+		return log10(1 + 1 / $k);
+	}
+
+	private function calculate() {
+		$this->benford = [];
+
+		foreach ($this->array as $k => $v) {
+			$s = (string) $v;
+			$this->benford[10][$s[0]]['keys'][] = $k;
+		}
+
+		foreach ($this->benford[10] as $k => $v) {
+			$this->benford[10][$k]['value'] = count($v['keys']) / count($this->array);
+			if ($this->benford[10][$k]['correct'] = ($this->benford[10][$k]['value'] <= $this->benford($k))) {
+				unset($this->benford[10][$k]['keys']);
+			} else {
+				$this->calculate100($k);
+			}
+		}
+
+		ksort($this->benford[10]);
+		ksort($this->benford[100]);
+	}
+
+	private function calculate100($a) {
+		foreach ($this->benford[10][$a]['keys'] as $k) {
+			$s = (string) $this->array[$k];
+			if (strlen($s) < 2) continue;
+			$this->benford[100][$a][$s[1]]['keys'][] = $k;
+		}
+
+		foreach ($this->benford[100][$a] as $k => $v) {
+			$this->benford[100][$a][$k]['value'] = count($v['keys']) / count($this->array);
+			if ($this->benford[100][$a][$k]['correct'] = ($this->benford[100][$a][$k]['value'] <= $this->benford($a * 10 + $k))) {
+				unset($this->benford[100][$a][$k]['keys']);
+			}
+		}
+
+		ksort($this->benford[100][$a]);
+		ksort($this->benford[100][$a]);
+	}
+
+	public function getResult() {
+		$this->calculate();
+		return $this->benford;
+	}
+}