Replace substrings with an incremented counter value

Question

Basically what I'm looking for is the PHP version of this thread: Find, replace, and increment at each occurence of string

I would like to replace the keyword following > at the start of rach line with an incrementing counter.

If my input is:

>num, blah, blah, blah

ATCGACTGAATCGA

>num, blah, blah, blah

ATCGATCGATCGATCG

>num, blah, blah, blah

ATCGATCGATCGATCG

I would like it to be...

>0, blah, blah, blah

ATCGACTGAATCGA

>1, blah, blah, blah

ATCGATCGATCGATCG

>2, blah, blah, blah

ATCGATCGATCGATCG

Joe · Accepted Answer · 2012-02-14 07:23:17Z

2

$str = 'a hello a some a';
$i = 0;

while (strpos($str, 'a') !== false)
{
    $str = preg_replace('/a/', $i++, $str, 1);
}

echo $str;

answered Feb 14, 2012 at 7:23

Joe

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1 Comment

mickmackusa Over a year ago

I don't support the use of iterated preg_replace() calls, but if you are going to use a technique like this, then you can eliminate the extra iterated strpos() calls and use the count reference variable from preg_replace() in the condition of a do-while loop like this: stackoverflow.com/a/64964297/2943403

va5ja · Accepted Answer · 2014-03-25 10:18:28Z

1

preg_replace(array_fill(0, 5, '/'.$findme.'/'), range(1, 5), $string, 1);

Example:

preg_replace(array_fill(0, 5, '/\?/'), range(1, 5), 'a b ? c ? d ? e f g ? h ?', 1);

Output

a b 1 c 2 d 3 e f g 4 h 5

answered Mar 25, 2014 at 10:18

va5ja

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1 Comment

mickmackusa Over a year ago

This unexplained snippet suffers the same lack of directness as Joe's answer. Every time preg_replace() processes a new element in the first parameter, it checks the full string from the start every time. This means that characters that were checked in previous sweeps are checked again while searching for the first remaining match.

mickmackusa · Accepted Answer · 2020-12-19 22:24:38Z

I prefer to use preg_replace_callback() for this task . It is a more direct solution than making iterated single preg_replace() calls which restart from the beginning of the string each time (checking text that has already been replaced).

^ means the start of a line because of the m pattern modifier.
\K means restart the full string match. This effectively prevents the literal > from being replaced and so only the literal string num is replaced.
the static counter declaration will only set $counter to 0 on the first visit.
the custom function does not need to receive the matched substring because the entire full string match is to be replaced.

Code: (Demo)

$text = <<<TEXT
>num, blah, blah, blah

ATCGACTGAATCGA

>num, blah, blah, blah

ATCGATCGATCGATCG

>num, blah, blah, blah

ATCGATCGATCGATCG
TEXT;

echo preg_replace_callback(
         "~^>\Knum~m",
         function () {
             static $counter = 0;
             return ++$counter;
         },
         $text
     );

Jordan Arsenault · Accepted Answer · 2012-02-14 07:40:45Z

0

If I understood your question properly...

<?php
//data resides in data.txt
$file = file('data.txt');
//new data will be pushed into here.
$new = array();
//fill up the array
foreach($file as $fK =>$fV) $new[] = (substr($fV, 0, 1)==">")? str_replace("num", $fK/2, $fV) : $fV;
//optionally print it out in the browser.
echo "<pre>";
print_r($new);
echo "</pre>";
//optionally write to file...
$output = fopen("output.txt", 'w');
foreach($new as $n) fwrite($output, $n);
fclose($output);

edited Feb 14, 2012 at 7:40

answered Feb 14, 2012 at 7:30

Jordan Arsenault

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2 Comments

mickmackusa Over a year ago

While this solution may work on the provided sample, it is not suitable for general use cases because str_replace() has no way of limiting its number of replacements. This means that the function may incorrectly replace substrings later in the qualifying line.

mickmackusa Over a year ago

The same can be said about dividing the indexes by two to calculate the desired number in the replacement -- it is just not suitable for general use cases.

Anand Sainath · Accepted Answer · 2012-02-14 08:23:09Z

-2

Here's my two cents

function str_replace_once($correct, $wrong, $haystack) {
    $wrong_string = '/' . $wrong . '/';
    return preg_replace($wrong_string, $correct, $haystack, 1);
}

The above function is used to replace the string occurence only once, but you are free to edit the function to perform every other possible operation.

answered Feb 14, 2012 at 8:23

Anand Sainath

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1 Comment

mickmackusa Over a year ago

This answer does not directly, specifically provide the desired output for the question asked and can be safely discarded from the pool of correct answers.

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