How to merge subarrays using keys and sum the values? - php

Question

I'm fairly new to PHP and I'm having some trouble with arrays and combining data. I have the following array which has been created from a foreach loop:
array(1) {
[36868]=> int(3)
}
array(1) {
[2112]=> int(3)
}
array(1) {
[35901]=> int(3)
}
array(1) {
[6496]=> int(3)
}
array(1) {
[87]=> int(3)
}
array(1) {
[36868]=> int(3)
}
array(1) {
[68]=> int(3)
}
array(1) {
[9068]=> int(3)
}
array(1) {
[47]=> int(3)
}
The key in each array is a user ID, so I need to preserve this, but I only want one instance of each key and where there are duplicate keys, sum the values. Like so:
array(1) {
[36868]=> int(6)
}
array(1) {
[2112]=> int(3)
}
array(1) {
[35901]=> int(3)
}
array(1) {
[6496]=> int(3)
}
array(1) {
[87]=> int(3)
}
array(1) {
[68]=> int(3)
}
array(1) {
[9068]=> int(3)
}
array(1) {
[47]=> int(3)
}
The I've tried looping through the array:
foreach ($array as $key => &$value) {
if ($value[0] == $value[1]) {
$value[1] += $value[1];
}
}
But with no luck. I've also tried rendering the arrays differently i.e. [userid]=>1,[score]=>3 and I feel like I'm going round in circles a bit, so any help would be hugely appreciated.

Answer 1

$data <-- this is your original array
$result = array_reduce(
$data,
function($carry, $item) {
foreach ($item as $id => $score) {
if (array_key_exists($id, $carry)) {
$carry[$id] += $score;
} else {
$carry[$id] = $score;
}
}
return $carry;
},
[]
);
If you are sure that each item only contains 1 entry you could also simplify the callback to not use foreach:
$result = array_reduce(
$data,
function ($carry, $item) {
$score = reset($item);
$id = key($item);
if (array_key_exists($id, $carry)) {
$carry[$id] += $score;
} else {
$carry[$id] = $score;
}
return $carry;
},
[]
);
You could also keep using foreach instead:
/** foreach to create a $data array like described below and afterwards do this: **/
$result = [];
foreach($data as $row) {
$score = reset($row);
$id = key($row);
if (array_key_exists($id, $result)) {
$result[$id] += $score;
} else {
$result[$id] = $score;
}
}
This will take an array $data like this:
array(
array('1' => 3),
array('1' => 3),
array('2' => 3),
);
and creates the variable $result like this:
array(
'1' => 6,
'2' => 3,
);

Answer 2

Here is a clean method that will not produce Notices. When merge-summing array data the efficient method is to generate temporary keys and use the very fast isset() function. I could have used current() and key() to access the lone subarray element, but the second foreach control structure is actually faster and more compact. (Ref:
https://stackoverflow.com/a/21219594/2943403 )
Code: (Demo)
$array = [
[36868 => 3],
[2112 => 3],
[35901 => 3],
[6496 => 3],
[87 => 3],
[36868 => 3],
[68 => 3],
[9068 => 3],
[47 => 3]
];
$result = [];
foreach ($array as $subarray) {
foreach ($subarray as $k => $v) {
if (!isset($result[$k])) {
$result[$k] = $subarray;
} else {
$result[$k][$k] += $v;
}
}
}
var_export(array_values($result));
Output:
array (
0 =>
array (
36868 => 6,
),
1 =>
array (
2112 => 3,
),
2 =>
array (
35901 => 3,
),
3 =>
array (
6496 => 3,
),
4 =>
array (
87 => 3,
),
5 =>
array (
68 => 3,
),
6 =>
array (
9068 => 3,
),
7 =>
array (
47 => 3,
),
)