preg_replace arrays with multiple patterns per replacement

Question

I don't think I can do this in one swell foop, but I'm not above asking :-)

I can certainly define one-to-one $pattern and $replacement arrays, and I can repeatedly define $pattern arrays and $replacement strings, but can I do both at once?

Suppose I have three sets like:

$p1 = array('sis','boom','bah');
$r1 = 'cheers';

$p2 = array('boo','hiss');
$r2 = 'jeers';

$p3 = array('guinness','heineken','budweiser');
$r3 = 'beers';

and I'd like to replace in a single large haystack all instances of patterns with their respective single replacements. Is there a single preg_replace call that I can define to accomplish this?

you can use (sis|boom|bah) in your pattern if you're using regular expressions, otherwise str_replace can take an array of values for the search and replace with a single value. — Scuzzy
– Scuzzy, Commented Jul 17, 2017 at 2:25
str_replace() will not respect word boundaries and may return unexpected results when a substring is found inside another substring. — mickmackusa
– mickmackusa ♦, Commented Jul 17, 2017 at 3:22
To fully expose the trouble with not including word boundaries... if you have $string='My sister paid 500 baht for a boomerang'; and use echo preg_replace('/sis|boom|bah/','cheers',$string); then you will get this mangled mess: My cheerster paid 500 cheerst for a cheerserang while there were no intended replacements to make. — mickmackusa
– mickmackusa ♦, Commented Jul 17, 2017 at 4:53

mickmackusa · Accepted Answer · 2017-07-17 02:52:24Z

I think you will need to incorporate word boundaries with a regex-based function.

Consider this strtr() demo:

$string="Rah rah, sis boom bah, I read a book on budweiser";
$p1 = array('sis','boom','bah');
$r1 = 'cheers';
$p2 = array('boo','hiss');
$r2 = 'jeers' ;
$p3 = array('guinness','heineken','budweiser');
$r3 = 'beers';

$replacements=array_merge(
    array_combine($p1,array_fill(0,sizeof($p1),$r1)),
    array_combine($p2,array_fill(0,sizeof($p2),$r2)),
    array_combine($p3,array_fill(0,sizeof($p3),$r3))
);
echo strtr($string,$replacements);

Output:

Rah rah, cheers cheers cheers, I read a jeersk on beers
//                                      ^^^^^ Oops

You will just need to implode your needle elements using pipes and wrap them in a non-capturing group so that the word boundaries apply to all substrings, like this:

Code: (Demo)

$string="Rah rah, sis boom bah, I read a book on budweiser";
$p1 = ['sis','boom','bah'];
$r1 = 'cheers';
$p2 = ['boo','hiss'];
$r2 = 'jeers' ;
$p3 = ['guinness','heineken','budweiser'];
$r3 = 'beers';
$find=['/\b(?:'.implode('|',$p1).')\b/','/\b(?:'.implode('|',$p2).')\b/','/\b(?:'.implode('|',$p3).')\b/'];
$swap=[$r1,$r2,$r3];
var_export($find);
echo "\n";
var_export($swap);
echo "\n";
echo preg_replace($find,$swap,$string);

Output:

array (
  0 => '/\\b(?:sis|boom|bah)\\b/',                 // unescaped: /\b(?:sis|boom|bah)\b/
  1 => '/\\b(?:boo|hiss)\\b/',                     // unescaped: /\b(?:boo|hiss)\b/
  2 => '/\\b(?:guinness|heineken|budweiser)\\b/',  // unescaped: /\b(?:guinness|heineken|budweiser)\b/
)
array (
  0 => 'cheers',
  1 => 'jeers',
  2 => 'beers',
)
Rah rah, cheers cheers cheers, I read a book on beers

*Notes:

The word boundaries \b ensure that whole words are match, avoiding unintended mismatches.

If you need case-insensitivity, just use the i flag at the end of each regex pattern. e.g. /\b(?:sis|boom|bah)\b/i

Aha! Yes, changing each array of patterns to a single regexp would reduce it to 1:1 again. That's a bit of a pain, but implode() is a cool trick that makes this programmatic again. I'll look forward to more ideas, but this probably gets the check mark when I can look again tomorrow :-) Thanks!

user10089632 · Accepted Answer · 2017-07-17 02:42:04Z

0

$subject = 'sis + boo + guinness';
echo preg_replace(['/sis|boom|bah/','/boo|hiss/','/guinness|heineken|budweiser/'],['cheers','jeers','beers'],$subject);
// the result would be cheers + jeers + beers

replacement The string or an array with strings to replace. If this parameter is a string and the pattern parameter is an array, all patterns will be replaced by that string. If both pattern and replacement parameters are arrays, each pattern will be replaced by the replacement counterpart. If there are fewer elements in the replacement array than in the pattern array, any extra patterns will be replaced by an empty string. ...

If subject is an array, then the search and replace is performed on every entry of subject, and the return value is an array as well.

edited Jul 17, 2017 at 2:42

answered Jul 17, 2017 at 2:26

user10089632

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3 Comments

mickmackusa Over a year ago

Your method yields an unintended result when boo is changed to book. sandbox.onlinephpfunctions.com/code/… See my answer regarding word boundaries.

user10089632 Over a year ago

@mickmackusa, in the link above $subject = 'sis + book + guinness'; resulted in cheers + jeersk + beers which is the normal expected behaviour,

mickmackusa Over a year ago

Not if you only want to replace the whole word boo instead of the start of book See what I mean?

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