ScatterGraph - repeated keys

The code below is the source for this graph.

<?php
// ScatterGraph - repeated keys
require_once 'SVGGraph/autoloader.php';

$settings = [
  'auto_fit' => true,
  'back_colour' => '#eee',
  'back_stroke_width' => 0,
  'back_stroke_colour' => '#eee',
  'stroke_colour' => '#000',
  'axis_colour' => '#111',
  'axis_overlap' => 2,
  'grid_colour' => '#999',
  'label_colour' => '#000',
  'axis_font' => 'Arial',
  'axis_font_size' => 12,
  'pad_bottom' => 5,
  'minimum_grid_spacing' => 20,
  'show_subdivisions' => true,
  'show_grid_subdivisions' => true,
  'grid_subdivision_colour' => '#ccc',
  'bar_label_colour' => '#fff',
  'bar_label_font_size' => 11,
  'structured_data' => true,
];

$type = 'ScatterGraph';
$width = 300;
$height = 200;
$colours = [ [ 'red', 'yellow' ], [ 'blue', 'white' ] ];

$values = [
  [1, 30], [1, 60], [2, 50], [3, 40],
  [3, 90], [6, 50], [6, 60], [7, 20]
];

$graph = new Goat1000\SVGGraph\SVGGraph($width, $height, $settings);
$graph->colours($colours);
$graph->values($values);

$graph->render($type);

Please note: the source code above comes from a script used to generate one of the example graphs on the site. This is simply a wrapper page to apply highlighting and make the source code easier to read, so there is no content here to describe what the source code is doing.