Robin Vickery escribió:
On 14/05/06, Gonzalo Monzón <gmc@xxxxxxxxxxxxx> wrote:
Satyam escribió:
> Of course, another possibility is that the author does not know how to
> handle multidimensional arrays (just to say it before anyone else
> points an obvious alternative)
>
I don't think the author does not know how to handle multidimensional
arrays. I thought the author was more concerned about performance than
other issues people like as coding "beautifuly"... Maybe author's
approach is weird, but its twice faster in the worst case!!
Sure the author only needs to loop the whole array and doesn't need
multi-dimensional approach... 'cause its a lot faster to iterate once
the array is filled!!
Look at the test I've done (below) its seems filling multi-dimensional
arrays is n/2 faster than single dimension, but then when you need to
read the array data, a multi-dimensional approach is always worse than
n*6!!
Your setup is odd. I get much more similar results with both php 4 and 5.
You're also using a more than slightly odd way of iterating through
the array.
These does exactly the same as your Test functions and are
considerably faster:
<?php
function Test_c() {
global $testC;
for ($a=1;$a<999;++$a) {
for ($b=1;$b<999;++$b) {
$testC[$a][$b] = $a . $b;
}
}
}
function Test_c2() {
global $testC;
foreach ($testC as $k => $v) {
foreach ($v as $k2 => $v2);
}
}
?>
Test results from PHP 5.0.5:
Fill style A, bidimensional array: 3.0747
Iteration style A, bidimensional array: 2.4385
Total time style A: 5.5135
Fill style B, single-dimension array: 4.6502
Iteration style B, single-dimension array: 2.3964
Total time style B: 7.047
Fill style C, bidimensional array: 2.5237
Iteration style C, bidimensional array, foreach loop: 1.3415
Total time style C: 3.8656
Test results from PHP 4.4.0:
Fill style A, bidimensional array: 3.2056
Iteration style A, bidimensional array: 2.3848
Total time style A: 5.5907
Fill style B, single-dimension array: 5.1468
Iteration style B, single-dimension array: 2.4016
Total time style B: 7.5488
Fill style C, bidimensional array: 2.6899
Iteration style C, bidimensional array, foreach loop: 1.4073
Total time style C: 4.0976
Hi Robin,
Don't thought my setup is odd. Only I can say my computer maybe isn't as
faster than yours. I use centrino mobile, windows xp, and test was run
on php 4.3.9 ( sorry i missed that, thought was 4.3.4)
I know it can be coded to be faster, but my point with that php snippet
was to compare the same "odd" way with single or multi dimensional
approaches. Sure $a.$b is faster than "$a$b" and foreach than do while
(the more if you didn't "use" each element datum!! that's hi -
optimization! does sense for you using foreach without assigning any
value from it? yes, you've got them inside foreach $v2 - $k2, but in my
code i've got too them inside key($v) $v[key($v)], and I do assign them
to another var, so if you want to compare performance, please to it too!
anyway I checked this and both multidimensional approaches performs
pretty equal. )
I didn't code that snippet to the best / faster execution methodology
for this individual case but a generic "odd" way for comparing both
cases. The same I did in python, as that language as far more adaptable
data structures for letting you choose the best for your case needs (I
could use python numarray (uses C arrays) and I thought you could't beat
it in PHP or any PHP C extension, but that's far from the purpose of my
posts.
If do I use $a.$b instead "$a$b" and assign each element key & val from
foreach in "type c" test, that's what I got: -see below- B & C perform
nearly equal on total time, of course, the best approach would be highly
dependent on the real data to use. The only I thing could say about your
foreach approach is I allways avoided using it in some kind of projects,
as it does a copy of the data on every iteration, so when using lots of
objects, huge data, or pass-per-reference had lot of memory performance
issues using it in php4 -Im speaking about very long-running scripts
where these issues really care- so do { } while(next()) is the only you
can use safely...
Notice huge gap in running the type A test in my computer and in yours
for php 4.4.0 - me 4.3.9, you get 5.59 and I got 13.9, and other tests
seems my install always performs better than yours! :-) (type b: you
5.12 - 2.40 = 7.54 me 4.08 - 1.66 = 5.57 that's about 2 secods!!). That
means to me so this test don't probe nothing, they are all very
variable... I don't know why that great difference, but I don't think
the php revision changes from 4.3.9 to 4.4.0 are relevant enought as for
these performance gaps. We should use a real tests library for choosing
best case of several runs, and so on...
Anyway these are the results using your test_c modified code with two
lines added... notice filling type A and C share the same code, and
there is some gap: 1,97 - 2,16 !
Fill style A, bidimensional array: 1,9726
Iteration style A, bidimensional array: 11,9345
Total time style A: 13,9319
Fill style B, single-dimension array: 4,0895
Iteration style B, single-dimension array: 1,664
Total time style B: 5,7598
Fill style C, bi-dimensional array: 2,1671
Iteration style C, bi-dimensional array: 3,6194
Total time style C: 5,7958
Regards,
Gonzalo
function Test_c2() {
global $testC;
foreach ($testC as $k => $v) {
foreach ($v as $k2 => $v2) {
->> $z = $k2;
->> $y = $v2;
}
}
}
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