Group associative row data based on shared column value - php

Question

I have a multidimensional array like:
Array
(
[0] => Array
(
[division] => Mymensingh
[A] => 1
)
[1] => Array
(
[division] => Dhaka
[A] => 5
)
[2] => Array
(
[division] => Mymensingh
[B] => 2
[C] => 5
)
)
I need to find the rows with matching division values and merge them in one array.
From this array, I want the output as:
Array
(
[0] => Array
(
[division] => Mymensingh
[A] => 1
[B] => 2
[C] => 5
)
[1] => Array
(
[division] => Dhaka
[A] => 5
)
)
Keys in the subarrays can be different and the subarrays may have a differing number of elements.

Answer 1

I think it's relatively simple to just iterate through the array and continuously merge the entries separated by "division":
function mergeByDiscriminator($input, $discriminator = 'division') {
$result = [];
foreach ($input as $array) {
$key = $array[$discriminator];
$result[$key] = array_merge(
array_key_exists($key, $result) ? $result[$key] : [],
$array
);
}
return array_values($result);
}
$result = mergeByDiscriminator($input); // $input is your array

Answer 2

The only solution that I can think of is as below. Of course there might be other feasable solutions, but I am giving one from my end.
$array = array(
'0' => array (
'division' => 'Mymensingh',
'A' => 1
),
'1' => array (
'division' => 'Dhaka',
'A' => 5
),
'2' => array (
'division' => 'Mymensingh',
'B' => 2,
'C' => 5
),
);
$result = array();
foreach ($array as $arr) {
if (!is_array($result[$arr['division']])) $result[$arr['division']] = array();
foreach ($arr as $key => $value) {
$result[$arr['division']][$key] = $value;
}
}
echo "<pre>"; print_r($result);
The above code is giving you the desired output. Please give it a try.
Hope this helps.

Answer 3

This task is concisely completed with zero iterated function calls thanks to the null coalescing operator and the union operator.
Merge each iterated row with the pre-existing data in that keyed-group. If the keyed-group has not yet been encountered merge the row with an empty array.
The union operator is suitable/reliable in this case because it is writing one associative array into another associative array.
Language Construct Iteration: (Demo)
$result = [];
foreach ($array as $row) {
$result[$row['division']] = ($result[$row['division']] ?? []) + $row;
}
var_export(array_values($result));
Functional Iteration: (Demo)
var_export(
array_values(
array_reduce(
$array,
function($result, $row) {
$result[$row['division']] = ($result[$row['division']] ?? []) + $row;
return $result;
},
[]
)
)
);