PhpBench\Math\Statistics::histogram PHP Method

    public static function histogram(array $values, $steps = 10, $lowerBound = null, $upperBound = null)
    {
        $min = $lowerBound ?: min($values);
        $max = $upperBound ?: max($values);
        $range = $max - $min;
        $step = $range / $steps;
        $steps++;
        // add one extra step to catch the max value
        $histogram = [];
        $floor = $min;
        for ($i = 0; $i < $steps; $i++) {
            $ceil = $floor + $step;
            if (!isset($histogram[(string) $floor])) {
                $histogram[(string) $floor] = 0;
            }
            foreach ($values as $value) {
                if ($value >= $floor && $value < $ceil) {
                    $histogram[(string) $floor]++;
                }
            }
            $floor += $step;
            $ceil += $step;
        }
        return $histogram;
    }

    public function generate(SuiteDocument $results, Config $config)
    {
        $document = new Document();
        $reportEl = $document->createRoot('reports');
        $reportEl->setAttribute('name', $config->getName());
        $reportEl = $reportEl->appendElement('report');
        $descriptionEl = $reportEl->appendElement('description');
        $descriptionEl->nodeValue = <<<EOT
Warning: The histogram report is experimental, it may change or be removed without warning in
future versions of PHPBench.
EOT;
        $tableEl = $reportEl->appendElement('table');
        foreach ($results->query('//subject') as $subjectEl) {
            foreach ($subjectEl->query('.//variant') as $variantEl) {
                $times = array();
                foreach ($variantEl->query('.//iteration') as $iterationEl) {
                    $times[] = $iterationEl->getAttribute('rev-time');
                }
                if (count($times) > 1) {
                    $histogram = Statistics::histogram($times, $config['bins']);
                    $kde = new Kde($times);
                    $kdeX = Statistics::linspace(min($times), max($times), $config['bins'] + 1);
                    $kdeY = $kde->evaluate($kdeX);
                } else {
                    $histogram = array((string) current($times) => 1);
                    $kdeY = array(null);
                }
                $counter = 0;
                foreach ($histogram as $xValue => $frequency) {
                    $kdeVal = $kdeY[$counter++];
                    $rowEl = $tableEl->appendElement('row');
                    $cellEl = $rowEl->appendElement('cell');
                    $cellEl->setAttribute('name', 'benchmark');
                    $cellEl->nodeValue = functions\class_name($subjectEl->evaluate('string(ancestor::benchmark/@class)'));
                    $cellEl = $rowEl->appendElement('cell');
                    $cellEl->setAttribute('name', 'subject');
                    $cellEl->nodeValue = $subjectEl->evaluate('string(./@name)');
                    $cellEl = $rowEl->appendElement('cell');
                    $cellEl->setAttribute('name', 'index');
                    $cellEl->nodeValue = $counter;
                    $cellEl = $rowEl->appendElement('cell');
                    $cellEl->setAttribute('name', 'time');
                    $cellEl->nodeValue = $xValue;
                    $cellEl = $rowEl->appendElement('cell');
                    $cellEl->setAttribute('name', 'freq');
                    $cellEl->nodeValue = $frequency;
                    $cellEl = $rowEl->appendElement('cell');
                    $cellEl->setAttribute('name', 'kde');
                    $cellEl->nodeValue = $kdeVal;
                }
            }
        }
        return $document;
    }