Avoid Nested Loop in PHP - php

Question

I am writing a method which takes an array of $topicNames and an array of $app and concatenates each $app to $topicNames like the following
public function getNotificationTopicByAppNames(array $topicNames, array $apps)
{
$topics = [];
foreach ($topicNames as $topicName) {
foreach ($apps as $app) {
$topic = $app . '_' . $topicName;
$topics[] = $topic;
}
}
return $topics;
}
}
The input and result are like the following...
$topicNames = [
'one_noti',
'two_noti',
'three_noti'
];
$apps = [
'one_app',
'two_app'
];
// The return result of the method will be like the following
[
'one_app_one_noti',
'two_app_one_noti',
'one_app_two_noti',
'two_app_two_noti',
'one_app_three_noti',
'two_app_three_noti'
]
My question is instead of doing nested loops, is there any other way I can do? Why do I want to avoid nested loops? Because currently, I have $topic. Later, I might want to add languages, locations etc...
I know I can use map, reduce, array_walks, each those are basically going through one by one. Instead of that which another alternative way I can use? I am okay changing different data types instead of the array as well.

Answer 1

If you dont care about the order you can use this
function getNotificationTopicByAppNames(array $topicNames, array $apps)
{
$topics = [];
foreach($apps as $app){
$topics = array_merge($topics, preg_filter('/^/', $app.'_', $topicNames));
}
return $topics;
}
print_r(getNotificationTopicByAppNames($topicNames,$apps));
Output
Array
(
[0] => one_app_one_noti
[1] => one_app_two_noti
[2] => one_app_three_noti
[3] => two_app_one_noti
[4] => two_app_two_noti
[5] => two_app_three_noti
)
Sandbox
You can also switch loops and use the $ instead to postfix instead of prefix. Which turns out to be in the same order you had. I thought of prefixing as a way to remove the loop. Then i thought why not flip it.
function getNotificationTopicByAppNames(array $topicNames, array $apps)
{
$topics = [];
foreach($topicNames as $topic){
$topics = array_merge($topics, preg_filter('/$/', '_'.$topic, $apps));
}
return $topics;
}
print_r(getNotificationTopicByAppNames($topicNames,$apps));
Output
Array
(
[0] => one_app_one_noti
[1] => two_app_one_noti
[2] => one_app_two_noti
[3] => two_app_two_noti
[4] => one_app_three_noti
[5] => two_app_three_noti
)
Sandbox
The trick here is using preg_filter.
http://php.net/manual/en/function.preg-filter.php
preg_filter — Perform a regular expression search and replace
So we search with ^ start or $ end which doesn't capture anything to replace and then we just add on what we want. I've used this before when I wanted to prefix a whole array with something, etc.
I couldn't test it in a class, so I made it a regular function, so adjust as needed.
Cheers!

Answer 2

You can use :
<?php
public function mergeStacks(...$stacks)
{
$allStacks = call_user_func_array('array_merge', $stacks);
return $this->concatString($allStacks);
}
private function concatString(&$stack, $index = 0, &$result = [])
{
if(count($stack) == 0){
return '';
}
if($index == count($stack)){
return $result;
}
array_walk($stack, function($value, $key) use($index, &$result, $stack){
if($key > $index){
array_push($result, $stack[$index] . '_' . $value);
}
});
$index = $index + 1;
return $this->concatString($stack, $index, $result);
}
And then when you want to get the array, no matter if you have languages or topics etc, you can just do :
$this->mergeStacks($languages, $topics, $locations, .....);
Where $languages, $topics, $locations are simple arrays.

Answer 3

Instead of accepting only topics name parameter try something like this:
function getNotificationTopicByAppNames(array $apps, array ...$names)
{
$topics = [];
foreach ($names as $nameArray) {
foreach ($nameArray as $topicName) {
foreach ($apps as $app) {
$topic = $app . '_' . $topicName;
$topics[] = $topic;
}
}
}
return $topics;
}
$topicNames = [
'one_noti',
'two_noti',
'three_noti'
];
$languagesNames = [
'test_en',
'test_other',
'test_other2'
];
$apps = [
'one_app',
'two_app'
];
print_r(getNotificationTopicByAppNames($apps,$topicNames,$languagesNames));
you can pass any number of arrays to array.