#20793 [Opn->Bgs]: big selection with array_rand() works bad EVEN with srand()
| From: | dave at arthistory dot cc | Date: | Tue, 03 Dec 2002 21:24:03 +0000 |
| Subject: | #20793 [Opn->Bgs]: big selection with array_rand() works bad EVEN with srand() | ||
| References: | 1 | Groups: | php.bugs |
| Request: | Send a blank email to php-bugs+get-26564@lists.php.net to get a copy of this message | ||
ID: 20793
User updated by: dave@arthistory.cc
Reported By: dave@arthistory.cc
-Status: Open
+Status: Bogus
Bug Type: Arrays related
Operating System: Linux (redhat6.2) 2.2.14-5.0smp
PHP Version: 4.2.3
New Comment:
I'm terrible sorry the cause is most certain mysqlbased, for some
reason the first 100'rows contains almost 50% of number betweens
1000-1152 (from a random selection of 1-1152) weird.
But the with the script:
$tempArrValue=1000;
$brickArray = array();
for($i=1;$i<=$tempArrValue;$i++){
$brickArray[$i]=$i;
}
srand ((float) microtime() * 10000000);
$brickArray2 = array_rand($brickArray, sizeof($brickArray));
$temp = 0;
for($i=0;$i<=250;$i++){
$temp = $temp + $brickArray2[$i];
}
echo $temp / 250;
I did get a correct answer, recieved number around 500.
Again I'm terrible sorry for taking your time, please contact me of you
want me to test something other, or anything else I can do.
Best Regards Dave
Previous Comments:
------------------------------------------------------------------------
[2002-12-03 12:35:39] msopacua@php.net
Here's something to test properly:
<?php
function printline($string)
{
static $nl = -1;
if($nl == -1)
$nl = (isset($_SERVER['REMOTE_ADDR'])) ? "<br />\n" :
"\n";
print("$string$nl");
}
$bricks = (isset($argv[1])) ? $argv[1] : 1;
if($bricks==1) $tempArrValue=450;
if($bricks==2) $tempArrValue=800;
if($bricks==3) $tempArrValue=1152;
$brickArray = array();
for($i=1;$i<=$tempArrValue;$i++){
$brickArray[$i]=$i;
}
srand ((float) microtime() * 10000000);
$brickArray2 = array_rand($brickArray, sizeof($brickArray));
for($i=0;$i<sizeof($brickArray2);$i++){
printline("$i => {$brickArray2[$i]}");
}
?>
I can't reproduce it - in fact, the following quick-hack-shell-tester
doesn't yield any output:
#!/bin/ksh
typeset -i COUNTER=1
while [ $COUNTER -lt 100 ]; do
./test_array_rand.php 3 | awk '{print $3}' | sort | perl -n -e
'print if $_ eq $previous; $previous=$_'
COUNTER=
expr ${COUNTER} + 1
done
You should probably look at the query, rather than at rand. But then
again - if the above yields output, report back.
------------------------------------------------------------------------
[2002-12-03 11:35:19] dave@arthistory.cc
I will test the snapshot this weekend, I have no access to a test
machine earlier
Ps, array_rand($brickArray, sizeof($brickArray)-3);
should be array_rand($brickArray, sizeof($brickArray));,
the error occur with both! Ds
------------------------------------------------------------------------
[2002-12-03 11:28:27] sniper@php.net
Please try using this CVS snapshot:
http://snaps.php.net/php4-latest.tar.gz
For Windows:
http://snaps.php.net/win32/php4-win32-latest.zip
------------------------------------------------------------------------
[2002-12-03 11:24:16] dave@arthistory.cc
http://www.arthistory.cc/info.php for my php info
------------------------------------------------------------------------
[2002-12-03 11:21:49] dave@arthistory.cc
I use array_rand() to randomize an array that can have three different
sizes, 450, 800 and 1152. With 450 array_rand works great. But when I
try to select 800 and 1152 indexes with array_rand(), array_rand seems
to seed higher number. I everycase I always get the 25 last indexes
picked! Pretty weird! It seems to favor the last number!
I have tried:
srand ((float) microtime() * 10000000);
srand ((float) microtime() * 1000000);
But that didn't helped:
Here's my code:
if($bricks==1) $tempArrValue=450;
if($bricks==2) $tempArrValue=800;
if($bricks==3) $tempArrValue=1152;
$brickArray = array();
for($i=1;$i<=$tempArrValue;$i++){
$brickArray[$i]=$i;
}
srand ((float) microtime() * 10000000);
$brickArray2 = array_rand($brickArray, sizeof($brickArray)-3);
for($i=0;$i<sizeof($brickArray2);$i++){
mysql_query("insert into puzzle_bricks values(0,$countryIndex,$i, " .
$brickArray2[$i] . ");");
}
My conclusion is that their are some problems when seeding random
numbers for array_rand when you are selecting an array with more than
800 indexes as output.
I mean I have solved the issue by making my own array_rand function,
but I just wanted to help makeing PHP a better product.
Best Regards Dave,
Ps, I love PHP, Ds
------------------------------------------------------------------------
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Edit this bug report at http://bugs.php.net/?id=20793&edit=1