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

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 polyline 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.?

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2

Answers


  1. 0

    Is this what you’re after? Updated

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

$mids = [];

foreach (array_values($points) as $k => $v) {
    if (!empty($points[$k+1])) {
        $x1 = $points[$k]['x'];
        $x2 = $points[$k+1]['x'];
        $y1 = $points[$k]['y'];
        $y2 = $points[$k+1]['y'];
        $mids[] = ['x' => ($x1 + $x2) / 2, 'y' => ($y1 + $y2) / 2];
    }
}

print_r($mids);

    output of this is

    Array
(
    [0] => Array
        (
            [x] => 30
            [y] => 15
        )

    [1] => Array
        (
            [x] => 45
            [y] => 35
        )

    [2] => Array
        (
            [x] => 65
            [y] => 32.5
        )

)
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  2. 0

    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);
}
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