Explain how this custom function works PHP

Question

Here this function in PHP that allows to merge any N amount of different length arrays in a fashion that output array will be in next order: Array1[0],Array2[0],..,Arr

Answer 1

The arrays $a, $b and $c have 10, 6 and 2 elements respectively.

$a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
$b = ['a', 'b', 'c', 'd', 'e', 'f'];
$c = ['A', 'B'];

When you feed the arrays as arguments for the array_zip_merge() function, look at the for loop. The func_get_args() will set the $args with all the arguments supplied. On start of first for loop run,

$args = [$a, $b, $c];
count($args) = 3;

At the foreach loop the array_shift will return the first element of each array resulting the $output to be like

$output = [1, 'a', 'A'];

And the arrays now look like,

$a = [2, 3, 4, 5, 6, 7, 8, 9, 10];
$b = ['b', 'c', 'd', 'e', 'f'];
$c = ['B'];

At the end of the first for loop the array_filter function will test if any array is empty and remove it from $args. Same thing will happen at the second run, and by the end of the second for loop, the variables would look like

$a = [3, 4, 5, 6, 7, 8, 9, 10];
$b = ['c', 'd', 'e', 'f'];
$c = [];
$output = $output = [1, 'a', 'A', 2, 'b', 'B'];
//because $c is empty array_filter() removes it from $args
$args = [$a, $b];

So, on the third iteration of the for loop count($args) will return 2. When the last element of $b has been removed by array_shift the count($args) will return 1. The iteration will continue until all the arrays are empty

Answer 2

Inside array_zip_merge, the for statement always takes the first values of each array and add them to output variable respectively.

Because array_shift removes the element it returns, on every loop the first elements are different. When it gets empty because of it, the loop has nothing to do and breaks.

If you still dont understand, ask the specific part of the code you have trouble with please.