Sorry, I believed that this function call should only return the spaces
segment:
preg_filter('/^( *)/', '${0}', ' <table>...</table>')
But it returns whole string ' <table>...</table>' instead of ' '
El 29/10/16 a les 09:50, Narcis Garcia ha escrit:
> preg_replace('/^( *)/', '${0}', ' <table>...</table>') ==
> ' <table>...</table>'
>
>
> El 29/10/16 a les 05:17, German Geek ha escrit:
>> OK, in the interest of science I implemented a test:
>>
>> The difference in performance is absolutely minimal:
>> 0.07233524322509943 micro seconds on a million iterations (0.795%). The
>> regex seemed to be winning with less iterations which I didn't expect, even
>> if regexes would be faster.
>>
>> *Conclusion: Just use regexes as string handling code can get complicated
>> fast and I think more complex regexes outperform complicated string
>> handling. Even just adding a character that is not trimmed by ltrim to this
>> makes the string handling really hard.*
>>
>> Note also, that the regex here might be compiled every time, in which case
>> regexes are the clear winner. I think PHP might cache the compiled regex
>> though.
>>
>> Result:
>> php regex.php
>> time for string: 9.1010239124298
>> time for regex: 9.1733591556549
>>
>> Code:
>> <?php
>>
>> define('LINE_LENGTH', 80);
>> define('ITERATIONS', 1000000);
>> function getSpaced() {
>> $amount = rand(0, LINE_LENGTH);
>> $nonSpaceAmount = rand(0, LINE_LENGTH);
>> $spaces = str_repeat(' ', $amount);
>> $rest = '';
>> for ($i = 0; $i < $nonSpaceAmount; ++$i) {
>> $rest .= chr(rand(ord('A'), ord('z')));
>> }
>> return $spaces . $rest;
>> }
>> $start = microtime(true);
>> for ($i = 0; $i < ITERATIONS; ++$i) {
>> $string = getSpaced();
>> substr($string, 0, strlen($string) - strlen(ltrim($string)));
>> }
>> echo "time for string: " . (microtime(true) - $start) . "\n";
>>
>> $start = microtime(true);
>> for ($i = 0; $i < ITERATIONS; ++$i) {
>> $string = getSpaced();
>> preg_match('/^( *)/', $string, $matches);
>> //$matches[1];
>> }
>> echo "time for regex: " . (microtime(true) - $start) . "\n";
>>
>>
>> On Sat, 29 Oct 2016 at 15:37 German Geek <geek.de@xxxxxxxxx> wrote:
>>
>>> String functions are very fast. Regexes have to be compiled under the hood
>>> to take advantage of their speed. PHP does this behind the scenes. So, if
>>> you are only looking for spaces it's going to run faster in my humble
>>> opinion.
>>>
>>> However, I agree that regexes are probably better in any case, because
>>> they are much more powerful and for someone who understands them, just as
>>> easy to read if not easier, especially in this example.
>>>
>>> The difference in performance is probably not noticeable, especially not
>>> nowadays. Saving developer time is more important and I would use regexes
>>> as well.
>>>
>>> I could be wrong about regexes being slower. It's just what I read
>>> somewhere. I guess one would have to do the test on a large input to verify
>>> on a case by case basis. As far as I understand regexes have to perform
>>> string functions also, which I think are probably more complicated than in
>>> this example. Again, something to test.
>>>
>>> I would want to know, just out of interest though. :-)
>>>
>>> On Sat, 29 Oct 2016 at 12:40 Ashley Sheridan <ash@xxxxxxxxxxxxxxxxxxxx>
>>> wrote:
>>>
>>>
>>>
>>> On 28 October 2016 23:33:00 BST, German Geek <geek.de@xxxxxxxxx> wrote:
>>>> regex is nicer, because it is less code and you can detect any white
>>>> space
>>>> etc.
>>>>
>>>> However!
>>>>
>>>> substring etc will be faster and more understandable to others who do
>>>> not
>>>> know much about regexes.
>>>>
>>>> On Sat, 29 Oct 2016 at 02:21 Christoph M. Becker <cmbecker69@xxxxxx>
>>>> wrote:
>>>>
>>>>> On 28.10.2016 at 14:51, Richard wrote:
>>>>>
>>>>>>> Date: Friday, October 28, 2016 12:09:31 +0100
>>>>>>> From: Ashley Sheridan <ash@xxxxxxxxxxxxxxxxxxxx>
>>>>>>>
>>>>>>> On 28 October 2016 12:01:16 BST, Narcis Garcia
>>>>>>> <informatica@xxxxxxxxx> wrote:
>>>>>>>
>>>>>>>> Hello, I have a string (I quote here only) as:
>>>>>>>>
>>>>>>>> ' <table>...</table>'
>>>>>>>>
>>>>>>>> As you can see there are 3 spaces at the beginning, but it could
>>>>>>>> be 0 or
>>>>>>>> 4 or any number of spaces.
>>>>>>>> How can I get a string with only the initial spaces part?
>>>>>>>>
>>>>>>>> ' <table>...</table>' -> ' '
>>>>>>>> 'hello' -> ''
>>>>>>>> ' hello' -> ' '
>>>>>>>>
>>>>>>>> Thanks.
>>>>>>>
>>>>>>> Have you tried regular expressions? Something like:
>>>>>>>
>>>>>>> ^( )*[^ ]
>>>>>>>
>>>>>>> The first captured match is the number of spaces, from 0 to any
>>>>>>> amount. Not the space between the brackets and before the closing
>>>>>>> square bracket
>>>>>>
>>>>>> You need to take into consideration that "whitespace" can be
>>>> created
>>>>>> by more than the simple "space" (ascii 32) character. A
>>>> "[horizontal]
>>>>>> tab" (ascii 9) is common, but also look at the top of php trim
>>>>>> function documentation:
>>>>>>
>>>>>> <http://php.net/manual/en/function.trim.php>
>>>>>>
>>>>>> to see the characters that it handles as "whitespace".
>>>>>
>>>>> If general whitespace should be detected with a regexp, \s could be
>>>> used.
>>>>>
>>>>>> While "trim"
>>>>>> does the opposite of what you're after, […]
>>>>>
>>>>> Indeed, so one could do something like
>>>>>
>>>>> substr($string, 0, strlen($string) - strlen(ltrim($string)))
>>>>>
>>>>> I'd prefer a regexp solution, though.
>>>>>
>>>>> --
>>>>> Christoph M. Becker
>>>>>
>>>>>
>>>>> --
>>>>> PHP General Mailing List (http://www.php.net/)
>>>>> To unsubscribe, visit: http://www.php.net/unsub.php
>>>>>
>>>>>
>>>
>>> I really don't think performing two strlen() calls, a substr(), & an
>>> ltrim() is going to be faster than a regular expression.
>>>
>>> I don't think you should avoid regex's because some people don't
>>> understand them. It's a very simple regular expression. You wouldn't tell
>>> someone to avoid PDO and use mysql_* functions because PDO is too
>>> complicated for some people would you?
>>> --
>>> Sent from my Android device with K-9 Mail. Please excuse my brevity.
>>>
>>>
>>
>
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