How could I remove duplicates of characters found in array $a from string $b only if they are found next to each other?
$a = array("a","b","c");
$b = "aabcccdef";
Output should be
abcdef
Characters can be found with a regex but I have no idea how to detect if the characters are next to each other.
preg_replace( array('/a+/','/b+/','/c+/'),array('a','b','c',), $b );
Another way pretty more elaborate could be:
preg_replace_callback('/(\w+)/', function ($matches) use ($a) {
if ( in_array($matches[1][0],$a) ) //> if you need UTF-8 working use mb_substr here
return $matches[1][0];
},$b);
//> both untested
Another way, old way (that could be a bit faster on few chars string):
$c = '';
$cache = false;
for ($i=0;$i<strlen($b);$i++) {
$char = $b[$i];
if ($char !== $cache || !in_array($char,$a))
$c .= $char;
$cache=$char;
}
echo $c;
Another way:
$expression = join('|', $a);
$b = preg_replace('/(' . $expression . ')\1+/', '$1', $b);
Explanation:
The generated expression will look like (a|b)\1+, where a|b matches either a or b. \1 matches whatever was matched by the first capture group (a|b). This is how you can match a set of repeating characters. The match then gets replaced by the content of the capture group ($1).
This would not only work with single characters but with any substrings.
If the strings can contain special regular expression characters, you should escape those characters first (array_map('preg_quote', $a) should work just fine).
<?php
$a = array('a', 'b', 'c');
$b = 'aabcccdef';
$c = '';
for($i = 0; $i < strlen($b); $i++) {
if(in_array($b[$i], $a) && (substr($c, -1) === $b[$i])) {
continue;
}
$c .= $b[$i];
}
echo $c;
