What is the PHP equivalent of JavaScript spread syntax for constructing an array?

Question

Asked already a question about converting functions from Ruby to JS, and now I'm trying to implement with JS to PHP, but something does not work, tell me what I'm missing?

The code on JS:

function transpose(a) {
    return a.length === 0 ? a : a[0].map((col, i) => a.map((row) => row[i]))
}

function f(a) {
    return a.length === 0 ? [] : [...a.shift(), ...f(transpose(a).reverse())];
} 

console.log(f([[1, 2, 3, 4], [12, 13, 14, 5], [11, 16, 15, 6], [10, 9, 8, 7]]))

In PHP do so:

function transpose($array) 
{
    if (count($array) === 0) return $array;

    foreach ($array as  $rowkey => $row)
    {
        foreach($row as $colkey => $col)
        {
            $out[$colkey][$rowkey] = $col;
        }
    }

    return $out;
}

function f($a)
{
    return (count($a) === 0) 
    ? [] 
    : [
        array_shift(...$a), 
        f(array_reverse(transpose(...$a)))
    ];
}

print_r(f([[1,2,3,4],[10,11,12,5],[9,8,7,6]]));

Is there a problem? Errors:

Warning: array_shift() expects exactly 1 parameter, 3 given in [...][...] on line 24

Invalid argument supplied for foreach() in [...][...] on line 10

Warning: Invalid argument supplied for foreach() in [...][...] on line 10

Warning: Invalid argument supplied for foreach() in [...][...] on line 10

Warning: Invalid argument supplied for foreach() in [...][...] on line 10

Notice: Undefined variable: out in [...][...] on line 16

Warning: array_reverse() expects parameter 1 to be array, null given in [...][...] on line 25 Warning: count(): Parameter must be an array or an object that implements Countable in [...][...] on line 21

Can you please add some more details about what you mean by "something does not work"? — Don't Panic
– Don't Panic, Commented Oct 22, 2018 at 21:25
You can't do that. As PHP is precompiled and JS is post compiled, you cannot do PHP from the JS side. — Forbs
– Forbs, Commented Oct 22, 2018 at 21:29
array_shift(...$a) should be ...array_shift($a) to be equivalent to the JS. — Barmar
– Barmar, Commented Oct 22, 2018 at 21:30

Don't Panic · Accepted Answer · 2018-10-22 21:50:25Z

4

You don't need to use the ... operator in the PHP version. You just need to merge the shifted row with the result of the recursive call.

function f($a)
{
    return (count($a) === 0) 
    ? [] 
    : array_merge(
        array_shift($a), 
        f(array_reverse(transpose($a)))
    );
}

array_merge(array_shift($a), f(array_reverse(transpose($a))))

is the same thing that's happening here:

[...a.shift(), ...f(transpose(a).reverse())]

... expands the elements of the array in JS. It works similarly in PHP, but here it is only valid in function definitions or calls.

edited Oct 22, 2018 at 21:50

answered Oct 22, 2018 at 21:34

Don't Panic

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Comments

Barmar · Accepted Answer · 2019-11-29 15:59:40Z

3

You have your ... (AKA "splat") operators in a different place in the PHP than the JS.

Also, prior to PHP 7.4 the splat operator can't be used in array literals, only in function calls. The use in the f() function is equivalent to array_merge().

function f($a)
{
    return (count($a) === 0) 
    ? [] 
    : array_merge(
        array_shift($a), 
        f(array_reverse(transpose($a)))
    );
}

DEMO

edited Nov 29, 2019 at 15:59

answered Oct 22, 2018 at 21:31

Barmar

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4 Comments

muesli Over a year ago

Parse error: syntax error, unexpected '...' (T_ELLIPSIS)

Barmar Over a year ago

You can't use ... in array literals, so I changed to a function call.

Rizky Arlin Over a year ago

php 7.4 now supports unpacking inside arrays. php.net/manual/en/migration74.new-features.php

Barmar Over a year ago

Thanks, I've added the caveat about 7.4 to the question.

Zak · Accepted Answer · 2018-10-22 21:36:34Z

1

Your array_shift has too many parameters .. All you need is the $a Same with array_reverse

<?php
function transpose($array)
{
    if (count($array) === 0) return $array;

    foreach ($array as  $rowkey => $row)
    {
        foreach($row as $colkey => $col)
        {
            $out[$colkey][$rowkey] = $col;
        }
    }

    return $out;
}

function f($a)
{
    return (count($a) === 0)
    ? []
    : [
        array_shift($a),
        f(array_reverse(transpose($a)))
    ];
}

print_r(f([[1,2,3,4],[10,11,12,5],[9,8,7,6]]));

RESULT

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

    [1] => Array
        (
            [0] => Array
                (
                    [0] => 5
                    [1] => 6
                )

            [1] => Array
                (
                    [0] => Array
                        (
                            [0] => 7
                            [1] => 8
                            [2] => 9
                        )

                    [1] => Array
                        (
                            [0] => Array
                                (
                                    [0] => 10
                                )

                            [1] => Array
                                (
                                    [0] => Array
                                        (
                                            [0] => 11
                                            [1] => 12
                                        )

                                    [1] => Array
                                        (
                                        )

                                )

                        )

                )

        )

)

edited Oct 22, 2018 at 21:36

answered Oct 22, 2018 at 21:31

Zak

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2 Comments

Barmar Over a year ago

This result isn't the same as the JavaScript version.

Barmar Over a year ago

It's supposed to return a flat array, not heavily nested.

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