str_repeat reverse (shrink strings) - php

Question

str_repeat(A, B) repeat string A, B times:
$string = "This is a " . str_repeat("test", 2) .
"! " . str_repeat("hello", 3) . " and Bye!";
// Return "This is a testtest! hellohellohello and Bye!"
I need reverse operation:
str_shrink($string, array("hello", "test"));
// Return "This is a test(x2)! hello(x3) and Bye!" or
// "This is a [test]x2! [hello]x3 and Bye!"
Best and efficient way for create str_shrink function?

Answer 1

Here are two versions that I could come up with.
The first uses a regular expression and replaces duplicate matches of the $needle string with a single $needle string. This is the most vigorously tested version and handles all possibilities of inputs successfully (as far as I know).
function str_shrink( $str, $needle)
{
if( is_array( $needle))
{
foreach( $needle as $n)
{
$str = str_shrink( $str, $n);
}
return $str;
}
$regex = '/(' . $needle . ')(?:' . $needle . ')+/i';
return preg_replace_callback( $regex, function( $matches) { return $matches[1] . '(x' . substr_count( $matches[0], $matches[1]) . ')'; }, $str);
}
The second uses string manipulation to continually replace occurrences of the $needle concatenated with itself. Note that this one will fail if $needle.$needle occurs more than once in the input string (The first one does not have this problem).
function str_shrink2( $str, $needle)
{
if( is_array( $needle))
{
foreach( $needle as $n)
{
$str = str_shrink2( $str, $n);
}
return $str;
}
$count = 1; $previous = -1;
while( ($i = strpos( $str, $needle.$needle)) > 0)
{
$str = str_replace( $needle.$needle, $needle, $str);
$count++;
$previous = $i;
}
if( $count > 1)
{
$str = substr( $str, 0, $previous) . $needle .'(x' . $count . ')' . substr( $str, $previous + strlen( $needle));
}
return $str;
}
See them both in action
Edit: I didn't realize that the desired output wanted to include the number of repetitions. I've modified my examples accordingly.

Answer 2

You can play around with tis one, not tested a lot though
function shrink($s, $parts, $mask = "%s(x%d)"){
foreach($parts as $part){
$removed = 0;
$regex = "/($part)+/";
preg_match_all($regex, $s, $matches, PREG_OFFSET_CAPTURE);
if(!$matches)
continue;
foreach($matches[0] as $m){
$offset = $m[1] - $removed;
$nb = substr_count($m[0], $part);
$counter = sprintf($mask, $part, $nb);
$s = substr($s, 0, $offset) . $counter . substr($s, $offset + strlen($m[0]));
$removed += strlen($m[0]) - strlen($part);
}
}
return $s;
}

Answer 3

I think you can try with:
<?php
$string = "This is a testtest! hellohellohello and Bye!";
function str_shrink($string, $array){
$tr = array();
foreach($array as $el){
$n = substr_count($string, $el);
$tr[$el] = $el.'(x'.$n.')';
$pattern[] = '/('.$el.'\(x'.$n.'\))+/i';
}
return preg_replace($pattern, '${1}', strtr($string,$tr));
}
echo $string;
echo '<br/>';
echo str_shrink($string,array('test','hello')); //This is a test(x2)! hello(x3) and Bye!
?>
I have a second version in order to works with strings:
<?php
$string = "This is a testtest! hellohellohello and Bye!";
function str_shrink($string, $array){
$tr = array();
$array = is_array($array) ? $array : array($array);
foreach($array as $el){
$sN = 'x'.substr_count($string, $el);
$tr[$el] = $el.'('.$sN.')';
$pattern[] = '/('.$el.'\('.$sN.'\))+/i';
}
return preg_replace($pattern, '${1}', strtr($string,$tr));
}
echo $string;
echo '<br/>';
echo str_shrink($string,array('test','hello')); //This is a test(x2)! hello(x3) and Bye!
echo '<br/>';
echo str_shrink($string,'test'); //This is a test(x2)! hellohellohello and Bye!
?>

Answer 4

I kept it short:
function str_shrink($haystack, $needles, $match_case = true) {
if (!is_array($needles)) $needles = array($needles);
foreach ($needles as $k => $v) $needles[$k] = preg_quote($v, '/');
$regexp = '/(' . implode('|', $needles) . ')+/' . ($match_case ? '' : 'i');
return preg_replace_callback($regexp, function($matches) {
return $matches[1] . '(x' . (strlen($matches[0]) / strlen($matches[1])) . ')';
}, $haystack);
}
The behavior of cases like str_shrink("aaa", array("a", "a(x3)")) is it returns "a(x3)", which I thought was more likely intended if you're specifying an array. For the other behavior, giving a result of "a(x3)(x1)", call the function with each needle individually.
If you don't want multiples of one to get "(x1)" change:
return $matches[1] . '(x' . (strlen($matches[0]) / strlen($matches[1])) . ')';
to:
$multiple = strlen($matches[0]) / strlen($matches[1]);
return $matches[1] . (($multiple > 1) ? '(x' . $multiple . ')' : '');

Answer 5

Here's a very direct, single-regex technique and you don't need to collect the words in the string in advance.
There will be some fringe cases to mitigate which are not represented in the sample input, but as for the general purpose of this task, I reckon this is the way that I'd script this in my project.
Match (and capture) any full word that is repeated one or more times.
Match the contiguous repetitions of the word.
Replace the fullstring match (substring of multiple words) with the captured first instance of the word.
Before returning the replacement string for re-insertion, add the desired formatting and calculate the number of repetitions by dividing the fullstring length by the captured string's length.
Code: (Demo)
$string = "This is a " . str_repeat("test", 2) .
"!\n" . str_repeat("hello", 3) . " and Bye!\n" .
"When I sleep, the thought bubble says " . str_repeat("zz", 3) . ".";
echo preg_replace_callback(
'~\b(\w+?)\1+\b~',
function($m) {
return "[{$m[1]}](" . (strlen($m[0]) / strlen($m[1])) . ")";
},
$string
);
Output:
This is a [test](2)!
[hello](3) and Bye!
When I sleep, the thought bubble says [z](6).
For a whitelist of needles, this adaptation to my above code does virtually the same job.
Code: (Demo)
function str_shrink($string, $needles) {
// this escaping is unnecessary if only working with alphanumeric characters
$needles = array_map(function($needle) {
return preg_quote($needle, '~');
}, $needles);
return preg_replace_callback(
'~\b(' . implode('|', $needles) . ')\1+\b~',
function($m) {
return "[{$m[1]}](" . (strlen($m[0]) / strlen($m[1])) . ")";
},
$string
);
}
echo str_shrink($string, ['test', 'hello']);
Output:
This is a [test](2)!
[hello](3) and Bye!
When I sleep, the thought bubble says zzzzzz.