Reform PHP associated array - php

Question

I have an associative array:
$input = [
['key'=>'x', 'value'=>'a'],
['key'=>'x', 'value'=>'b'],
['key'=>'x', 'value'=>'c'],
['key'=>'y', 'value'=>'d'],
['key'=>'y', 'value'=>'e'],
['key'=>'z', 'value'=>'f'],
['key'=>'m', 'value'=>'n'],
];
And I want to reform it simple in:
$output = [
'x'=>['a','b','c'],
'y'=>['d','e'],
'z'=>'f',
'm'=>'n'
]
So basically, conditions are:
1. If same key found then put values in an array.
2. If no same key found then value remains string.
You can replace associative array with object if you are more comfortable with objects.
Here is my working solution for this problem:
foreach($input as $in){
if(!empty($output[$in['key']])){
if(is_array($output[$in['key']])){
$output[$in['key']][] = $in['value'];
continue;
}
$output[$in['key']] = [$output[$in['key']],$in['value']];
continue;
}
$output[$in['key']] = $in['value'];
}
print_r($output);
However I believe that it can be done in much compact and efficient way.
Please comment your answers if someone has better solution.
Your help is much appreciated!

Answer 1

Reformat array to [ [ x=>a ], [x=>b],.. ] and merge all sub-arrays
$input = array_map(function($x) { return [$x['key'] => $x['value']]; }, $input);
$input = array_merge_recursive(...$input);
print_r($input);
demo

Answer 2

I would suggest
<?php
$input = [
['key'=>'x', 'value'=>'a'],
['key'=>'x', 'value'=>'b'],
['key'=>'x', 'value'=>'c'],
['key'=>'y', 'value'=>'d'],
['key'=>'y', 'value'=>'e'],
['key'=>'z', 'value'=>'f'],
['key'=>'m', 'value'=>'n'],
];
$reducer = function($carry, $item) {
$carry[$item['key']][] = $item['value'];
return $carry;
};
$mapper = function ($item) {
if (count($item) === 1) {
return $item[0];
}
return $item;
};
$output = array_map($mapper, array_reduce($input, $reducer, []));
var_dump($output);
You can see the result here: https://3v4l.org/8JjjS

Answer 3

You can use array_reduce to loop over an existing array and build up a new one:
$output = array_reduce($input, function ($carry, $i) {
$carry[$i['key']][] = $i['value'];
return $carry;
}, []);
Each element in $input is passed to the anonymous function, along with the $carry variable that's being built up as we go along. Inside, we just add each value to a sub-element indexed by key. The third argument [] is to set the initial value of the result to an empty array.
See https://eval.in/935015
(I'm assuming that the duplicate x keys in the question are a typo, and that the second is supposed to z, since that matches up with your suggested output)

Answer 4

For your original code you may find extract() interesting. I replaced the continue-s with else-s, but that is more like a matter of taste:
foreach($input as $in){
extract($in);
if(!empty($output[$key])){
if(is_array($output[$key])){
$output[$key][] = $value;
} else {
$output[$key] = [$output[$key],$value];
}
} else {
$output[$key] = $value;
}
On a side note I would probably use two much simpler loops, one for building lists and another for extracting single elements:
foreach($input as $in){
$output[$in['key']][] = $in['value'];
/* or: extract($in);
$output[$key][]=$value; */
}
foreach($output as $key => $value){
if(count($value)==1){
$output[$key]=$value[0];
}
}