Summation of array elements by the indexer [duplicate] - php

Question

I have an array of subarrays in the following format:
[
'a' => ['id' => 20, 'name' => 'chimpanzee'],
'b' => ['id' => 40, 'name' => 'meeting'],
'c' => ['id' => 20, 'name' => 'dynasty'],
'd' => ['id' => 50, 'name' => 'chocolate'],
'e' => ['id' => 10, 'name' => 'bananas'],
'f' => ['id' => 50, 'name' => 'fantasy'],
'g' => ['id' => 50, 'name' => 'football']
]
And I would like to group it into a new array based on the id field in each subarray.
array
(
10 => array
(
e => array ( id = 10, name = bananas )
)
20 => array
(
a => array ( id = 20, name = chimpanzee )
c => array ( id = 20, name = dynasty )
)
40 => array
(
b => array ( id = 40, name = meeting )
)
50 => array
(
d => array ( id = 50, name = chocolate )
f => array ( id = 50, name = fantasy )
g => array ( id = 50, name = football )
)
)

Answer 1

$arr = array();
foreach ($old_arr as $key => $item) {
$arr[$item['id']][$key] = $item;
}
ksort($arr, SORT_NUMERIC);

Answer 2

foreach($array as $key => $value){
$newarray[$value['id']][$key] = $value;
}
var_dump($newarray);
piece of cake ;)

Answer 3

The following code adapts #Tim Cooper’s code to mitigate Undefined index: id errors in the event that one of the inner arrays doesn’t contain an id:
$arr = array();
foreach($old_arr as $key => $item)
{
if(array_key_exists('id', $item))
$arr[$item['id']][$key] = $item;
}
ksort($arr, SORT_NUMERIC);
However, it will drop inner arrays without an id.
E.g.
$old_arr = array(
'a' => array ( 'id' => 20, 'name' => 'chimpanzee' ),
'b' => array ( 'id' => 40, 'name' => 'meeting' ),
'c' => array ( 'id' => 20, 'name' => 'dynasty' ),
'd' => array ( 'id' => 50, 'name' => 'chocolate' ),
'e' => array ( 'id' => 10, 'name' => 'bananas' ),
'f' => array ( 'id' => 50, 'name' => 'fantasy' ),
'g' => array ( 'id' => 50, 'name' => 'football' ),
'h' => array ( 'name' => 'bob' )
);
will drop the 'h' array completely.

Answer 4

You can also use Arrays::groupBy() from ouzo-goodies:
$groupBy = Arrays::groupBy($array, Functions::extract()->id);
print_r($groupBy);
And result:
Array
(
[20] => Array
(
[0] => Array
(
[id] => 20
[name] => chimpanzee
)
[1] => Array
(
[id] => 20
[name] => dynasty
)
)
[40] => Array
(
[0] => Array
(
[id] => 40
[name] => meeting
)
)
[50] => Array
(
[0] => Array
(
[id] => 50
[name] => chocolate
)
[1] => Array
(
[id] => 50
[name] => fantasy
)
[2] => Array
(
[id] => 50
[name] => football
)
)
[10] => Array
(
[0] => Array
(
[id] => 10
[name] => bananas
)
)
)
And here are the docs for Arrays and Functions.

Answer 5

Here is a function that will take an array as the first argument and a criteria (a string or callback function) as the second argument. The function returns a new array that groups the array as asked for.
/**
* Group items from an array together by some criteria or value.
*
* #param $arr array The array to group items from
* #param $criteria string|callable The key to group by or a function the returns a key to group by.
* #return array
*
*/
function groupBy($arr, $criteria): array
{
return array_reduce($arr, function($accumulator, $item) use ($criteria) {
$key = (is_callable($criteria)) ? $criteria($item) : $item[$criteria];
if (!array_key_exists($key, $accumulator)) {
$accumulator[$key] = [];
}
array_push($accumulator[$key], $item);
return $accumulator;
}, []);
}
Here is the given array:
$arr = array(
'a' => array ( 'id' => 20, 'name' => 'chimpanzee' ),
'b' => array ( 'id' => 40, 'name' => 'meeting' ),
'c' => array ( 'id' => 20, 'name' => 'dynasty' ),
'd' => array ( 'id' => 50, 'name' => 'chocolate' ),
'e' => array ( 'id' => 10, 'name' => 'bananas' ),
'f' => array ( 'id' => 50, 'name' => 'fantasy' ),
'g' => array ( 'id' => 50, 'name' => 'football' )
);
And examples using the function with a string and a callback function:
$q = groupBy($arr, 'id');
print_r($q);
$r = groupBy($arr, function($item) {
return $item['id'];
});
print_r($r);
The results are the same in both examples:
Array
(
[20] => Array
(
[0] => Array
(
[id] => 20
[name] => chimpanzee
)
[1] => Array
(
[id] => 20
[name] => dynasty
)
)
[40] => Array
(
[0] => Array
(
[id] => 40
[name] => meeting
)
)
[50] => Array
(
[0] => Array
(
[id] => 50
[name] => chocolate
)
[1] => Array
(
[id] => 50
[name] => fantasy
)
[2] => Array
(
[id] => 50
[name] => football
)
)
[10] => Array
(
[0] => Array
(
[id] => 10
[name] => bananas
)
)
)
Passing the callback is overkill in the example above, but using the callback finds its use when you pass in an array of objects, a multidimensional array, or have some arbitrary thing you want to group by.

Answer 6

Maybe it's worth to mention that you can also use php array_reduce function
$items = [
['id' => 20, 'name' => 'chimpanzee'],
['id' => 40, 'name' => 'meeting'],
['id' => 20, 'name' => 'dynasty'],
['id' => 50, 'name' => 'chocolate'],
['id' => 10, 'name' => 'bananas'],
['id' => 50, 'name' => 'fantasy'],
['id' => 50, 'name' => 'football'],
];
// Grouping
$groupedItems = array_reduce($items, function ($carry, $item) {
$carry[$item['id']][] = $item;
return $carry;
}, []);
// Sorting
ksort($groupedItems, SORT_NUMERIC);
print_r($groupedItems);
https://www.php.net/manual/en/function.array-reduce.php

Answer 7

Because of how PHP's sorting algorithm treats multidimensional arrays -- it sorts by size, then compares elements one at a time, you can actually use a key-preserving sort on the input BEFORE restructuring. In functional style programming, this means that you don't need to declare the result array as a variable.
Code: (Demo)
asort($array);
var_export(
array_reduce(
array_keys($array),
function($result, $k) use ($array) {
$result[$array[$k]['id']][$k] = $array[$k];
return $result;
}
)
);
I must say that functional programming is not very attractive for this task because the first level keys must be preserved.
Although array_walk() is more succinct, it still requires the result array to be passed into the closure as a reference variable. (Demo)
asort($array);
$result = [];
array_walk(
$array,
function($row, $k) use (&$result) {
$result[$row['id']][$k] = $row;
}
);
var_export($result);
I'd probably recommend a classic loop for this task. The only thing the loop needs to do is rearrange the first and second level keys. (Demo)
asort($array);
$result = [];
foreach ($array as $k => $row) {
$result[$row['id']][$k] = $row;
}
var_export($result);
To be completely honest, I expect that ksort() will be more efficient than pre-loop sorting, but I wanted to a viable alternative.