PHP - preg_replace on an array not working as expected - php

Question

I have a PHP array that looks like this..
Array
(
[0] => post: 746
[1] => post: 2
[2] => post: 84
)
I am trying to remove the post: from each item in the array and return one that looks like this...
Array
(
[0] => 746
[1] => 2
[2] => 84
)
I have attempted to use preg_replace like this...
$array = preg_replace('/^post: *([0-9]+)/', $array );
print_r($array);
But this is not working for me, how should I be doing this?

Answer 1

You've missed the second argument of preg_replace function, which is with what should replace the match, also your regex has small problem, here is the fixed version:
preg_replace('/^post:\s*([0-9]+)$/', '$1', $array );
Demo: https://3v4l.org/64fO6

Answer 2

You don't have a pattern for the replacement, or a empty string place holder.
mixed preg_replace ( mixed $pattern , mixed $replacement , mixed $subject)
Is what you are trying to do (there are other args, but they are optional).
$array = preg_replace('/post: /', '', $array );
Should do it.
<?php
$array=array("post: 746",
"post: 2",
"post: 84");
$array = preg_replace('/^post: /', '', $array );
print_r($array);
?>
Array
(
[0] => 746
[1] => 2
[2] => 84
)

Answer 3

You could do this without using a regex using array_map and substr to check the prefix and return the string without the prefix:
$items = [
"post: 674",
"post: 2",
"post: 84",
];
$result = array_map(function($x){
$prefix = "post: ";
if (substr($x, 0, strlen($prefix)) == $prefix) {
return substr($x, strlen($prefix));
}
return $x;
}, $items);
print_r($result);
Result:
Array
(
[0] => 674
[1] => 2
[2] => 84
)

Answer 4

There are many ways to do this that don't involve regular expressions, which are really not needed for breaking up a simple string like this.
For example:
<?php
$input = Array( 'post: 746', 'post: 2', 'post: 84');
$output = array_map(function ($n) {
$o = explode(': ', $n);
return (int)$o[1];
}, $input);
var_dump($output);
And here's another one that is probably even faster:
<?php
$input = Array( 'post: 746', 'post: 2', 'post: 84');
$output = array_map(function ($n) {
return (int)substr($n, strpos($n, ':')+1);
}, $input);
var_dump($output);
If you don't need integers in the output just remove the cast to int.
Or just use str_replace, which in many cases like this is a drop in replacement for preg_replace.
<?php
$input = Array( 'post: 746', 'post: 2', 'post: 84');
$output = str_replace('post: ', '', $input);
var_dump($output);

Answer 5

You can use array_map() to iterate the array then strip out any non-digital characters via filter_var() with FILTER_SANITIZE_NUMBER_INT or trim() with a "character mask" containing the six undesired characters.
You can also let preg_replace() do the iterating for you. Using preg_replace() offers the most brief syntax, but regular expressions are often slower than non-preg_ techniques and it may be overkill for your seemingly simple task.
Codes: (Demo)
$array = ["post: 746", "post: 2", "post: 84"];
// remove all non-integer characters
var_export(array_map(function($v){return filter_var($v, FILTER_SANITIZE_NUMBER_INT);}, $array));
// only necessary if you have elements with non-"post: " AND non-integer substrings
var_export(preg_replace('~^post: ~', '', $array));
// I shuffled the character mask to prove order doesn't matter
var_export(array_map(function($v){return trim($v, ': opst');}, $array));
Output: (from each technique is the same)
array (
0 => '746',
1 => '2',
2 => '84',
)
p.s. If anyone is going to entertain the idea of using explode() to create an array of each element then store the second element of the array as the new desired string (and I wouldn't go to such trouble) be sure to:
split on or : (colon, space) or even post: (post, colon, space) because splitting on : (colon only) forces you to tidy up the second element's leading space and
use explode()'s 3rd parameter (limit) and set it to 2 because logically, you don't need more than two elements