Inserting an item after specific array pattern - php

Question

I would like to insert an item after a specific pattern. In my case I would like to insert x after every second a in an array. After six'th a my code does not work properly:
$array = array("a","a","a","a","a","a","b","a","a");
$out = array();
foreach ($array as $key=>$value){
$out[] = $value; // add current letter to new array
if($value=='a' && $array[$key-1]=='a' && $out[$key] !='x'){ // check if current and last letter are a
$out[] = 'x'; // if so add an x to the array
}
}
print_r($out);

Answer 1

Correct answer at the end
Is it that what are you looking for?
<?php
$array = array("a","a","a","a","a","a","b","a","a");
foreach ($array as $key => $value){
if ($key == 0 || $key == 1) {
$array[$key] = $value;
} elseif($array[$key-1] == 'a' && $array[$key-2] == 'a' && $array[$key] == 'a') {
$array[$key] = 'x';
} else {
$array[$key] = $value;
}
}
$count = count($array);
if ($array[$count-1] == 'a' && $array[$count-2] == 'a') {
$array[] = 'x';
}
print_r($array);
?>
If I understand correctly, after 2 a you want to put x into new array.
UPDATE
Please check now. There will be added a new element x if last two are a in array.
With exceptions, but still working:
<?php
$array = array("a","a","a","a","a","a","b","a","a");
foreach ($array as $key => $value){
if($array[$key-1] == 'a' && $array[$key-2] == 'a' && $array[$key] == 'a') {
$array[$key] = 'x';
}
}
$count = count($array);
if ($array[$count-1] == 'a' && $array[$count-2] == 'a') {
$array[] = 'x';
}
print_r($array);
?>
UPDATE - Correct code
I think code below will fit all your needs:
<?php
$arr = array("a","w","a","d","a","a","b","a","a", "w");
$arr_count = count($arr);
for ($i = 0; $i < $arr_count; $i++){
if (!empty($arr[$i+1]) && $arr[$i] == $arr[$i+1]) {
$first_half = array_slice($arr, 0, $i+2);
$second_half = array_slice($arr, $i+2, $arr_count);
if (count($second_half) > 0) {
$arr = array_merge($first_half, ["x"], $second_half);
}
}
}
$count = count($arr);
if ($arr[$count-1] == 'a' && $arr[$count-2] == 'a') {
$arr[] = 'x';
}
print_r($arr);
?>

Answer 2

As it was mentioned in the comment, you sure can use regular expression in this particular situation:
$pattern = '/a{2}/';
$replacement = '$0x';
$out = str_split(preg_replace(
$pattern,
$replacement,
implode('', $array)
));
Basically, we gluing the characters together (using implode) to form the string and then replacing every "aa" with "aax". After that we split string back to the array using str_split.
Here is demo.