speed questions

[yawnmoth]

say i was trying to append a % before any occurance of either abc,
abd, or abe, in a string. which would be faster?:

$string = str_replace("ab c","%abc",$stri ng);
$string = str_replace("ab d","%abd",$stri ng);
$string = str_replace("ab e","%abe",$stri ng);

or

$string - preg_replace("/(abc|abd|abe)/","%$1",$string );

php.net says that preg_replace is slower than one str_replace, but for
multiple ones, it seems like it would gain a slight speed advantage.

also, exactly how would the following to code segments compare, speed
wise?

for ($num=0;$num<$l ength;$num++) {
$array1[] = $num;
$array2[] = $num;
}

for ($num=0;$num<$l ength;$num++)
$array1[] = $num;
for ($num=0;$num<$l ength;$num++)
$array2[] = $num;

it seems like the first one should require 3*$length operations,
whereas the first one would require 4*$length operations, although i'm
not 100% sure on that.

[Chris Hope]

Re: speed questions

yawnmoth wrote:
[color=blue]
> say i was trying to append a % before any occurance of either abc,
> abd, or abe, in a string.  which would be faster?:
>
> $string = str_replace("ab c","%abc",$stri ng);
> $string = str_replace("ab d","%abd",$stri ng);
> $string = str_replace("ab e","%abe",$stri ng);
>
> or
>
> $string - preg_replace("/(abc|abd|abe)/","%$1",$string );[/color]

Write a test script and run it in a loop say 1000 times doing the firstand
then the second and measure it. That'll tell you which is faster.

--
Chris Hope - The Electric Toolbox - http://www.electrictoolbox.com/

[rush]

Re: speed questions

"yawnmoth" <terra1024@yaho o.com> wrote in message
news:7j15d010pe bu1tuk3qmtepshu j1jhtcf12@4ax.c om...[color=blue]
> say i was trying to append a % before any occurance of either abc,
> abd, or abe, in a string. which would be faster?:
>
> $string = str_replace("ab c","%abc",$stri ng);
> $string = str_replace("ab d","%abd",$stri ng);
> $string = str_replace("ab e","%abe",$stri ng);
>
> or
>
> $string - preg_replace("/(abc|abd|abe)/","%$1",$string );
>
> php.net says that preg_replace is slower than one str_replace, but for
> multiple ones, it seems like it would gain a slight speed advantage.[/color]

you can also call str_replace with arrays of strings as parameters.

$string = str_replace(arr ay("abc","abd", "abe") ,
array("%abc","% abd","%abe"), $string);

rush
--

http://www.templatetamer.com/

[Christian Fersch]

Re: speed questions

yawnmoth wrote:[color=blue]
> say i was trying to append a % before any occurance of either abc,
> abd, or abe, in a string. which would be faster?:
>
> $string = str_replace("ab c","%abc",$stri ng);
> $string = str_replace("ab d","%abd",$stri ng);
> $string = str_replace("ab e","%abe",$stri ng);
>
> or
>
> $string - preg_replace("/(abc|abd|abe)/","%$1",$string );[/color]

A correct preg_replace will be the fastest.
$string = preg_replace("/(ab[cde])/","%$1",$string );

This will be a bit slower than one str_replace, and a lot faster than 3
of them.

[color=blue]
> also, exactly how would the following to code segments compare, speed
> wise?
>
> for ($num=0;$num<$l ength;$num++) {
> $array1[] = $num;
> $array2[] = $num;
> }
>
> for ($num=0;$num<$l ength;$num++)
> $array1[] = $num;
> for ($num=0;$num<$l ength;$num++)
> $array2[] = $num;
>
> it seems like the first one should require 3*$length operations,
> whereas the first one would require 4*$length operations, although i'm
> not 100% sure on that.[/color]

fastest here:
$array1 = $array2 = range(0,$length );

;)

greetings, Christian.

[Chung Leong]

Re: speed questions

"yawnmoth" <terra1024@yaho o.com> wrote in message
news:7j15d010pe bu1tuk3qmtepshu j1jhtcf12@4ax.c om...[color=blue]
> say i was trying to append a % before any occurance of either abc,
> abd, or abe, in a string. which would be faster?:
>
> $string = str_replace("ab c","%abc",$stri ng);
> $string = str_replace("ab d","%abd",$stri ng);
> $string = str_replace("ab e","%abe",$stri ng);
>
> or
>
> $string - preg_replace("/(abc|abd|abe)/","%$1",$string );
>
> php.net says that preg_replace is slower than one str_replace, but for
> multiple ones, it seems like it would gain a slight speed advantage.[/color]

I always like strtr(). Looks neater and doesn't involve the regexp engine.

$table = array(
"abc" => "%abc",
"abd" => "%abd",
"abe" => "%abe"
);
$string = strtr($string, $table);
[color=blue]
> also, exactly how would the following to code segments compare, speed
> wise?
>
> for ($num=0;$num<$l ength;$num++) {
> $array1[] = $num;
> $array2[] = $num;
> }
>
> for ($num=0;$num<$l ength;$num++)
> $array1[] = $num;
> for ($num=0;$num<$l ength;$num++)
> $array2[] = $num;
>[/color]

The correct answer is $array1 = $array2 = range(0, $length - 1);