create transpose matrix using php [duplicate] - php

Question

This question already has answers here:
Transposing multidimensional arrays in PHP
(12 answers)
Closed 2 years ago.
For example if a matrix is:
1 2
3 4
5 6
Then transpose of above matrix will be:
1 3 5
2 4 6
This is my current code:
<?php
// transpose matrix
$trans = array(
array(1, 2),
array(3, 4),
array(5, 6)
);
foreach ($trans as $key => $val){
foreach ($trans[$key] as $k => $v){
echo $v;
}
}
?>

Answer 1

There's a quirky PHP way to transpose a 2d array:
$trans = array(
array(1, 2),
array(3, 4),
array(5, 6)
);
array_unshift($trans, null);
$trans = call_user_func_array('array_map', $trans);
var_dump($trans);
Demo
EDIT Easier approach using PHP 5.6 array unpacking
With the introduction of the array argument unpacking feature in PHP 5.6, we can simplify this still further:
$trans = array(
array(1, 2),
array(3, 4),
array(5, 6)
);
$trans = array_map(null, ...$trans);
var_dump($trans);
EDIT Explanation
Quoting from the PHP docs for the array_map() function:
An interesting use of this function is to construct an array of arrays, which can be easily performed by using NULL as the name of the callback function
(See Example #4 from that docs page for an example of what this does)
The array_unshift($trans, null) that we perform first is providing that NULL callback, and we use call_user_func_array() because we don't necessarily know how many values there are in our $trans array. What we're doing using that call_user_func_array() is the equivalent of:
$trans = array_map(NULL, $trans[0], $trans[1], $trans[2]);
for your example array, because the top-level of your 2-d array has three elements (keys 0, 1 and 2).
Effectively, this NULL callback loops through all the arrays in parallel taking each value from them in turn to build a new array:
$maxArraySize = max(count($array[0], $array[1], $array[2]);
// $maxArraySize will have a value of 2 in your case,
// because your sub-arrays are all equal size
$newArray = [];
for($i = 0; $i < $maxArraySize; ++$i) {
$tmpArray = [];
$tmpArray[] = $array[0][$i];
$tmpArray[] = $array[1][$i];
$tmpArray[] = $array[2][$i];
$newArray[] = $tmpArray[];
}
There's a couple of extra checks in there
it doesn't care if your arrays are associative or enumerated in either dimension, because it accesses the $ith element, not the index
If the sub-arrays aren't all the same length, then it effectively pads the shorter sub-arrays with null values to match the length of the longest
It doesn't matter how many arrays you pass in, it will work with them all in parallel

Answer 2

I believe this works with rectangular arrays as well.
The trick: return array_map(null, ...$squareArray); seems to work in an unexpected way for a single column array
function RotateSquare2DArray($squareArray)
{
if ($squareArray == null) { return null; }
$rotatedArray = array();
$r = 0;
foreach($squareArray as $row) {
$c = 0;
if (is_array($row)) {
foreach($row as $cell) {
$rotatedArray[$c][$r] = $cell;
++$c;
}
}
else $rotatedArray[$c][$r] = $row;
++$r;
}
return $rotatedArray;
}
If the array is associative, I use this
function RotateSquareAssociativeArray($squareArray)
{
if ($squareArray == null) { return null; }
$rotatedArray = array();
$r = 0;
foreach($squareArray as $c=>$row) {
if (is_array($row)) {
foreach($row as $key=>$cell) {
$rotatedArray[$key][$c] = $cell;
}
}
else {
$rotatedArray[$c][$r] = $row;
}
++$r;
}
return $rotatedArray;
}