<?php
 
$initialArray = [
	'a' => [
		[0, 1, 2, 3, 4, 5, 6, 7],
		[8, 9, 10, 11, 12, 13, 14, 15],
		[16, 17, 18, 19, 20, 21, 22, 23],
		[24, 25, 26, 27, 28, 29, 30, 31]
	],
	'b' => [
		[10, 11, 12, 13, 14, 15, 16, 17],
		[18, 19, 110, 111, 112, 113, 114, 115],
		[116, 117, 118, 119, 120, 121, 122, 123],
		[124, 125, 126, 127, 128, 129, 130, 131]
	]
];
 
$array = array_map(function (array $firstLevelArray) {
	$newFirstLevelArray = array_map(function (array $secondLevelArray) {
		$newSecondLevelArray = array_map(function ($val) {
			return 2 * $val;
		}, $secondLevelArray);
		return implode(',', $newSecondLevelArray);
	}, $firstLevelArray);
 
	return implode('::', $newFirstLevelArray);
}, $initialArray);
 
$array = implode(';;;;', $array);
 
echo $array;

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