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Php – Replace last value in each row of a 2d array with the product of all values in the row excluding the last

Array ( 
[0] => Array ( [0] => 4 [1] => 3 [2] => 5 [3] => 7 [4] => 210 ) 
[1] => Array ( [0] => 4 [1] => 9 [2] => 5 [3] => 7 [4] => 210 ) 
[2] => Array ( [0] => 4 [1] => 9 [2] => 25 [3] => 7 [4] => 210 ) )

I would like to replace the last entry of each array with the product of the values from its preceding elements. For example,

Array ( [0] => 4 [1] => 3 [2] => 5 [3] => 7 [4] => 210 )

Would actually be:

Array ( [0] => 4 [1] => 3 [2] => 5 [3] => 7 [4] => 420 )

How do I delete that last element and multiply the preceding elements and fill in the correct value as the last element?

I tried reading about array_splice(), but do not understand the integer they used eg; array_splice($input, 1, -1);

Tags:

2

Answers


  1. 0

    A compact solution: array_walk() processes every row of the main array, the callable receives the sub-array as reference, removes the last element, calculates the product of all remaining elements using array_reduce() and assigns it as the last element of the sub-array.

    <?php

$mainArray = [
    
    [4, 3, 5, 7, 210],
    [4, 9, 5, 7, 210],
    [4, 9, 25, 7, 210],
];


array_walk ($mainArray, function (&$subArr) {
                           array_pop($subArr);
                           $subArr[] = !$subArr ? 0 : array_reduce($subArr, fn ($carry, $item) => $carry * $item, 1);
                        },
);


print_r ($mainArray);

    Result:

    Array
(
    [0] => Array
        (
            [0] => 4
            [1] => 3
            [2] => 5
            [3] => 7
            [4] => 420
        )

    [1] => Array
        (
            [0] => 4
            [1] => 9
            [2] => 5
            [3] => 7
            [4] => 1260
        )

    [2] => Array
        (
            [0] => 4
            [1] => 9
            [2] => 25
            [3] => 7
            [4] => 6300
        )
)
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  2. 0

    As you iterate the rows, isolate all but the last element and multiply them. Overwrite the last element with that product. (Demo)

    var_export(
    array_map(
        function($row) {
            $row[array_key_last($row)] = array_product(array_slice($row, 0, -1));
            return $row;
        },
        $array
    )
);

    Or multiply everything, then divide by the popped-off element: (Demo)

    var_export(
    array_map(
        function($row) {
            $row[] = array_product($row) / array_pop($row);
            return $row;
        },
        $array
    )
);

    Or remove the last element before multiplying (Demo)

    var_export(
    array_map(
        function($row) {
            array_pop($row);
            $row[] = array_product($row);
            return $row;
        },
        $array
    )
);

    Or enjoy arrow function syntax by uniting the product to the modified row: (Demo)

    var_export(
    array_map(
        fn($row) => $row + [array_key_last($row) => array_product($row) / array_pop($row)],
        $array
    )
);

    Or modify by reference using a classic loop: (Demo)

    foreach ($array as &$row) {
    array_pop($row);
    $row[] = array_product($row);
}
var_export($array);
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