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PHP – How can I loop through an array to compare consecutive values including first and last values

April 4, 2024

The following array contains a list of coordinates that I’m using to draw a polygon with ImageMagick:

$points = [
    ['x' => 40, 'y' => 10],
    ['x' => 20, 'y' => 20],
    ['x' => 70, 'y' => 50],
    ['x' => 60, 'y' => 15],
];

What I want to do is loop through this array and calculate the mid-point of each line segment by comparing each consecutive pair of coordinates including the first and last set i.e. the check must wrap-around either at the start or end of the loop. Is there a way to do this programatically without a lot of kludgey code to count the number of elements in the array and if() tests to determine when the first or last element has been reached, etc.?

>Solution :

Use modulus to wrap around to 0 at the end.

$midpoints = [];
$len = count($points);
foreach ($points as $i => $point1) {
    $point2 = $points[($i+1) % $len];
    $midpoints[] = get_midpoint($point1, $point2);
}