5.50. Example - Box Plot with Data Reduction
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## 5.50. Example - Box Plot with Data Reduction

This is a box plot (plot type boxes), without outliers. This example also shows how a PHP function might be used to create a PHPlot data array from experimental results. The input data is a series of lists of test results, and the output is a PHPlot data array for a box plot, with rows in the form `(label, Ymin, YQ1, Ymid, YQ3, Ymax)`.

Note: Box plots were added in PHPlot-6.1.0.

Example 5.50. Box Plot with Data Reduction

    <?php
    # PHPlot Example - Box Plot (without outliers)
    require_once 'phplot.php';

    # The experimental results:
    $results = array(
        'Material A1' => array(11.1, 8.4, 11.9, 13, 10.2, 9.2),
        'Material A2' => array(10.6, 9.8, 9.1, 12, 8.5, 7.1, 8.2, 7.8, 11.8),
        'Material B1' => array(9.9, 11.2, 10.9, 12.9, 8.5),
        'Material C1' => array(10.1, 11.8, 11.6, 8.5, 9.6, 12, 12, 8.9, 12.7, 10.3, 11.1),
        'Material C2' => array(10.9, 11.9, 7.3, 11.7, 12.6, 9.2, 10, 7, 7.1),
        'Material C3' => array(11.9, 9.1, 10.5, 10.7, 10, 7.3, 10.1, 11.7, 10.4, 9),
        'Material D1' => array(12, 8, 9.8, 11.4, 10.5, 12.5, 7.1, 8.6, 7.6, 7.4, 8.2, 7.1),
        'Material E1' => array(10.6, 8.2, 8.2, 7.9, 12, 7, 9.3),
    );

    # Return the k-th percentile value of a sorted array, where 0 <= $k <= 1
    # If there is no single value, return the average of the two adjacent ones.
    # Caution: Don't copy this code. It may not be valid, but suits the example.
    function kpercentile($row, $k)
    {
        $n = count($row);
        $p = $k * ($n - 1);
        if ($p == (int)($p)) return $row[$p];
        return ($row[(int)$p] + $row[(int)($p+1)]) / 2;
    }

    # Convert the experimental results to a PHPlot data array.
    function reduce_data($results)
    {
        $data = array();
        foreach ($results as $label => $row) {
            $n_samples = count($row);
            sort($row);
            $data[] = array("$label\n($n_samples Samples)",
                             $row[0],                  // Minimum
                             kpercentile($row, 0.25),  // Q1 = 25%
                             kpercentile($row, 0.50),  // Median
                             kpercentile($row, 0.75),  // Q3 = 75%
                             $row[$n_samples-1]);      // Maximum
        }
        return $data;
    }

    $plot = new PHPlot(800, 600);
    $plot->SetTitle('Box Plot (without outliers)');
    $plot->SetDataType('text-data');
    $plot->SetDataValues(reduce_data($results));
    $plot->SetPlotType('boxes');
    # These 2 lines make tick marks line up with text-data data points:
    $plot->SetXTickIncrement(1);
    $plot->SetXTickAnchor(0.5);
    $plot->SetImageBorderType('plain'); // Improves presentation in the manual
    $plot->DrawGraph();

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