5.12. Example - Points Plot / Scatterplot
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## 5.12. Example - Points Plot / Scatterplot

This is a rather contrived example of using a 'points' plot to make a scatterplot. The data array is a set of X/Y points. With 'points' plots, the data can be in any order and duplicate X values are allowed. The points here are generated from R = 0.5 * Theta.

For this example, the X and Y axes and tick marks were moved to 0,0, labels turned off, and plot borders enabled for all four sides.

Example 5.12. Points Plot / Scatterplot

    <?php
    # PHPlot Example: Point plot - scatter plot
    require_once 'phplot.php';

    $data = array();
    $a = 0.5;
    $d_theta = M_PI/48.0;
    for ($theta = M_PI * 7; $theta >= 0; $theta -= $d_theta)
      $data[] = array('', $a * $theta * cos($theta), $a * $theta * sin($theta));

    $plot = new PHPlot(800, 600);
    $plot->SetImageBorderType('plain');

    $plot->SetPlotType('points');
    $plot->SetDataType('data-data');
    $plot->SetDataValues($data);

    # Main plot title:
    $plot->SetTitle('Scatterplot (points plot)');

    # Need to set area and ticks to get reasonable choices.
    $plot->SetPlotAreaWorld(-12, -12, 12, 12);
    $plot->SetXTickIncrement(2);
    $plot->SetYTickIncrement(2);

    # Move axes and ticks to 0,0, but turn off tick labels:
    $plot->SetXAxisPosition(0); # Is default
    $plot->SetYAxisPosition(0);
    $plot->SetXTickPos('xaxis');
    $plot->SetXTickLabelPos('none');
    $plot->SetYTickPos('yaxis');
    $plot->SetYTickLabelPos('none');

    # Turn on 4 sided borders, now that axes are inside:
    $plot->SetPlotBorderType('full');

    # Draw both grids:
    $plot->SetDrawXGrid(True);
    $plot->SetDrawYGrid(True);  # Is default

    $plot->DrawGraph();

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5.11. Example - Points Plot with Error Bars | Home | 5.13. Example - Squared Plot