How to join similar elements of array with PHP - php

Question

We are running a PHP code on a huge list (array with 5 millions elements).
The list format is as follows below (it looks "weird" at first look but this is the best format so far we came out in order to optimize the speed of the code down below)
$array = array(
array(1 => true,3 => true),
array(2 => true,4 => true,6 => true),
array(3 => true,5 => true),
array(5 => true),
array(4 => true,8 => true,10 => true),
array(200 => true,300 => true)
);
We want to combine similar elements from the array above and get to this result:
$final_array = array(
array(1,3,5),
array(2,4,6,8,10),
array(200,300)
);
Instead of using array(1,3) we decided to use array(1 => true,3 => true) because using keys instead of values (to store information) makes the code below runs faster and it outputs $final_array as above.
foreach ($array as $key1 => $value1) {
foreach ($array as $key2 => $value2) {
if ($key1 != $key2) {
foreach ($array[$key1] as $key3 => $value3) {
if (isset($array[$key2][$key3])) {
$array[$key2] = $array[$key2] + $array[$key1];
unset($array[$key1]);
break 2;
}
}
}
}
}
However this code above is still very slow. Could you find a better way to aggregate similar elements to each other on a faster code?

Answer 1

How about using array_intersect_key instead of third loop?
$array = array(
array(1 => true,3 => true),
array(2 => true,4 => true,6 => true),
array(3 => true,5 => true),
array(5 => true),
array(4 => true,8 => true,10 => true),
array(200 => true,300 => true)
);
foreach ($array as $key => $value) {
foreach ($array as $key2 => $value2) {
if ($key !== $key2 && !empty(array_intersect_key($value, $value2))) {
$array[$key] = $value2 + $value;
unset($array[$key2]);
}
}
}
print_r($array);
Working example
Edit #1:
For better performance try this variant:
$array = array(
array(1 => true,3 => true),
array(2 => true,4 => true,6 => true),
array(3 => true,5 => true),
array(5 => true),
array(4 => true,8 => true,10 => true),
array(200 => true,300 => true)
);
$count = count($array);
for ($i = 0; $i < $count - 1; ++$i) {
for ($j = $i + 1; $j < $count; ++$j) {
if (!empty(array_intersect_key($array[$i], $array[$j]))) {
$array[$j] = $array[$i] + $array[$j];
unset($array[$i]);
continue 2;
}
}
}
Working example #2

Answer 2

$arr = array('Hello','World!','Beautiful','Day!');
echo join(" ",$arr);
See Details