Change data with preg_replace_callback function

Question

I have a file with some data in the format of:

0101    Group1  01/13/13
0102    Group1  02/03/13
0103    Group1  03/05/13
0104    Group1  04/05/13
0201    Group2  04/19/13
0202    Group2  05/10/13
0301    Group3  07/13/13
0302    Group3  07/13/13
0303    Group3  07/13/13
0401    Group4  02/12/13
0501    Group5  05/29/13

I only have a total of 5 Groups. I am trying to replace each Group with a single letter value here.

Group1 will be replaced with A
Group2 will be replaced with B
Group3 will be replaced with C
Group4 will be replaced with D
Group5 will be replaced with E

I found a way to do this with preg_replace_callback.

$text = preg_replace_callback('/Group[1-5]/', 'id_callback', $text);

function id_callback($matches) {
  if ($matches[0] == 'Group1') {
    return 'A';
  } elseif ($matches[0] == 'Group2') {
    return 'B';
  } elseif ($matches[0] == 'Group3') {
    return 'C';
  } elseif ($matches[0] == 'Group4') {
    return 'D';
  } elseif ($matches[0] == 'Group5') {
    return 'E';
  }
}

echo $text;

Is there a way I can do this and get rid of all these if statements?

Niet the Dark Absol · Accepted Answer · 2013-10-19 20:29:45Z

2

Mathematical relationships are a great help.

$text = preg_replace_callback("/Group([1-5])/",function($m) {
    return chr(ord("A")+$m[1]-1);
},$text);

answered Oct 19, 2013 at 20:29

Niet the Dark Absol

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2 Comments

user557846 Over a year ago

neat, i was writing an answer using an array, but this is cuter

Anthony Sterling Over a year ago

There shouldn't be a place for "Cute" in programming IMO, clarity is where the beauty is at. :)

Community · Accepted Answer · 2017-05-23 11:50:14Z

2

A different approach for this would incline using an associative array with either an anonymous/named function leading to running the callback for every match that it finds and populating the match with the value from the array.

$map = array('Group1' => 'A', 'Group2' => 'B', 
             'Group3' => 'C', 'Group4' => 'D', 'Group5' => 'E');

$text = preg_replace_callback('/(?P<id>Group[1-5])/', 
      function($m) {
          global $map; 
          extract($m);
          return isset($map[$id]) ? $map[$id] : $m[0];
      }, $text);

Note: I replaced your regular expression with a Named capturing Group for readabilty.

Update

As mentioned by @Niet the Dark Absol, here's a simple way to perform this using strtr to replace.

$text = _replace($text);

function _replace($t) {
  $map = array('Group1' => 'A', 'Group2' => 'B', 
               'Group3' => 'C', 'Group4' => 'D', 'Group5' => 'E'
  );
  return strtr($t, $map);
}

edited May 23, 2017 at 11:50

CommunityBot

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answered Oct 19, 2013 at 20:33

hwnd

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3 Comments

Guillaume Poussel Over a year ago

Instead of global, you can use function($m) use ($map) syntax for anonymous functions.

Niet the Dark Absol Over a year ago

If you're starting with the associative array, why not use the cheaper strtr to perform the swap?

hwnd Over a year ago

Thanks, I forgot about that

Casimir et Hippolyte · Accepted Answer · 2013-10-19 20:30:40Z

1

Yes:

$find = array('Group1', 'Group2', 'Group3', 'Group4', 'Group5');
$replace = array('A', 'B', 'C', 'D', 'E');
$result = str_replace($find, $replace, $string);

answered Oct 19, 2013 at 20:30

Casimir et Hippolyte

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