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

Points Plot / Scatterplot Example
# 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);


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

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

# Move axes and ticks to 0,0, but turn off tick labels:
$plot->SetXAxisPosition(0); # Is default

# Turn on 4 sided borders, now that axes are inside:

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


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