CODEWITHSUNDEEP
phppreg-replace
siaooo
siaooo

Reputation: 1825

preg_replace() versus preg_filter()

What are the differences between preg_replace() and preg_filter()?

In which situations should I use one instead of the other?

I tried reading the documentation, but still don't quite understand what the differences are.

Upvotes: 7

Views: 4399

Answers (3)

mickmackusa
mickmackusa

Reputation: 47894

  1. Both functions can process string-type (well, scalar-type values) input or a flat array and are primarily designed to return string or array type data -- depending on the input data-type. If preg_filter() receives a string but it does not satisfy the regex logic, then null will be returned. With either function, if there is an error, null will be returned.

  2. preg_replace() will mutate the data, but has no ability to remove elements; the only reason to ever use preg_filter() is when you wish to mutate the input value(s) AND remove the unaffected value(s).

  3. preg_filter() behaves like preg_replace() followed by a destructive step where unaffected values are either removed from the array or the string is converted to null. Like preg_replace(), preg_filter() has the ability to optionally limit replacements per string and count the number of replacements performed in the entire process.

Array test: (Demo)

$array = [
    "💩 happens",
    "I'm getting too old for this 💩",
    "shiitake",
    "Mondays are 💩, Tuesdays are 💩, and so on!",
    "Here is your Finnish itinerary",
    "Is this chocolate or 💩?"
];
var_export(
    preg_filter('/💩/u', 'poop', $array, 1, $count)  // parameters 4 and 5 are optional
);
echo "\n---\ncount: $count";

Output:

array (
  0 => 'poop happens',
  1 => 'I\'m getting too old for this poop',
  3 => 'Mondays are poop, Tuesdays are 💩, and so on!',
  5 => 'Is this chocolate or poop?',
)
---
count: 4

String Tests: (Demo)

var_export(
    preg_filter('/💩/u', 'poop', "Mondays are 💩, Tuesdays are 💩, and so on!", 1, $count)
);
echo "\n---\ncount: $count\n===\n";

var_export(
    preg_filter('/💩/u', 'poop', "shiitake", 1, $count)
);
echo "\n---\ncount: $count";

Output:

'Mondays are poop, Tuesdays are 💩, and so on!'
---
count: 1
===
NULL
---
count: 0

Upvotes: 0

Geoffrey
Geoffrey

Reputation: 5432

The advantage of preg_filter over preg_replace is that you can check whether or not anything was replaced, because preg_filter returns null if nothing was replaced, while preg_replace returns the subject regardless.

$subject = 'chips';
$pattern = '/chops/';
$replacement = 'flops';

if (is_null(preg_filter($pattern, $replacement, $subject)) { // true
    // do something
}

echo preg_replace($pattern, $replacement, $subject); // 'chips'

Upvotes: 2

DonCallisto
DonCallisto

Reputation: 29912

preg_filter() is identical to preg_replace() except it only returns the (possibly transformed) subjects where there was a match. For details about how this function works, read the preg_replace() documentation.

from: here

So if the signature is 

preg_filter ( mixed $pattern , mixed $replacement , 
              mixed $subject [, int $limit = -1 [, int &$count ]] )

it returns the $subject arguments "transformed" (all the match with regex pattern are substitute) into an array

Upvotes: 1

Related Questions