array_rand, not really random... is there a better way to grab a random line?

inVINCEable · April 18, 2009

Hey everyone,

Ok, So I have a program that generates random paragraphs of sentences arranged in files. Each file has about 30 sentences, and I am generating a random sentence from each file. The only problem is, it does not appear to be random at all. After about 15 random paragraph generations, I get the EXACT same order as one previously generated. I must be doing something wrong because the probability of this happening is about 1:9,000,000,000,000, and it has happened two days in a row, about six times. Please take a look at this simple script and offer some advice, it would be greatly appreciated. Perhaps I am just not seeding the random number generator properly?

Who knows, thanks again!

<html>

<head>


<?php
//EDIT BELOW

$current_name = "Linda"; 
$postingemail = "linda.clark+";


$title = array_map("trim", file("title.txt"));
$titlepost = $title[array_rand($title)];

$intro = array_map("trim", file("intro.txt"));
$intropost = $intro[array_rand($intro)];

$token1 = array_map("trim", file("token1.txt"));
$token1post = $token1[array_rand($token1)];

$token2 = array_map("trim", file("token2.txt"));
$token2post = $token2[array_rand($token2)];

$token3 = array_map("trim", file("token3.txt"));
$token3post = $token3[array_rand($token3)];

//
//here is where we start the custom stuff that was not included
//
$token4 = array_map("trim", file("token4.txt"));
$token4post = $token4[array_rand($token4)];

$token5 = array_map("trim", file("token5.txt"));
$token5post = $token5[array_rand($token5)];

$token6 = array_map("trim", file("token6.txt"));
$token6post = $token6[array_rand($token6)];

$token7 = array_map("trim", file("token7.txt"));
$token7post = $token7[array_rand($token7)];

$token8 = array_map("trim", file("token8.txt"));
$token8post = $token8[array_rand($token8)];

$token9 = array_map("trim", file("token9.txt"));
$token9post = $token9[array_rand($token9)];

$token11 = array_map("trim", file("token11.txt"));
$token11post = $token11[array_rand($token11)];

$token12 = array_map("trim", file("token12.txt"));
$token12post = $token12[array_rand($token12)];

$token13 = array_map("trim", file("token13.txt"));
$token13post = $token13[array_rand($token13)];

$token14 = array_map("trim", file("token14.txt"));
$token14post = $token14[array_rand($token14)];

$token15 = array_map("trim", file("token15.txt"));
$token15post = $token15[array_rand($token15)];

$token16 = array_map("trim", file("token16.txt"));
$token16post = $token16[array_rand($token16)];

$token17 = array_map("trim", file("token17.txt"));
$token17post = $token17[array_rand($token17)];



$email = array_map("trim", file("email.txt"));
$emailpost = $email[array_rand($email)];
$emailpost = str_replace("%name%", $current_name, $emailpost); 


$price = array_map("trim", file("price.txt"));
$pricepost = $price[array_rand($price)];

//EDIT ABOVE

$number[]="1";
$number[]="2";
$number[]="3";
$number[]="4";
$number[]="5";
$number[]="6";
$number[]="7";
$number[]="8";
$number[]="9";

$numberpost = $number[array_rand($number)];
$numberpost1 = $number[array_rand($number)];
$numberpost2 = $number[array_rand($number)];
$numberpost3 = $number[array_rand($number)];
$numberpost4 = $number[array_rand($number)];

?>

<style>
body {
background-color:#000000; 
color:white;
}
</style>
</head>

<body>

<center>
<br><form><input type=button value="REFRESH" onClick="window.location.reload()">
  <br>
</form> 
<h2>CL Account </h2>
<textarea name="textarea_head" id="textarea" cols="100" rows="1" onClick="this.focus(); this.select();">
<?php echo $postingemail; ?><?php echo $numberpost?><?php echo $numberpost1?><?php echo $numberpost2?><?php echo $numberpost3?><?php echo $numberpost4?>@gmail.com
</textarea>

<br>

<h2>Ad Title </h2>
<textarea name="textarea_head" id="textarea" cols="100" rows="1" onClick="this.focus(); this.select();">
<?php echo $titlepost?>
</textarea>
<br><br>

<h2>Price </h2>
<textarea name="textarea_head" id="textarea" cols="100" rows="1" onClick="this.focus(); this.select();">
<?php echo $pricepost?>
</textarea>
<br><br>

<h2>Ad Body</h2>
<textarea name="textarea_head" id="textarea" cols="100" rows="20" onClick="this.focus(); this.select();">
<?php echo $intropost?> <?php echo $token1post?> <?php echo $token2post?>
<br><br>
<b><?php echo $token3post?></b><br>
- <?php echo $token6post?><br>
- <?php echo $token7post?><br>
- <?php echo $token8post?><br>
- <?php echo $token9post?><br>
- <?php echo $token11post?><br>
- <?php echo $token12post?><br>
- <?php echo $token13post?><br>
- <?php echo $token14post?><br>
- <?php echo $token4post?><br><br>

<u><?php echo $token17post?></u><br>
- <?php echo $token16post?><br>
- <?php echo $token15post?><br>
- <?php echo $token5post?><br>


<br>
<?php echo $emailpost?>

</textarea>
</body>

laffin · April 18, 2009

From PHP.NET

Reinoud Elhorst
10-Apr-2007 10:50

Please note that (at least in PHP 4.3.11), while each key from the source array has a equal chance of being picked, the order in which they are returned is NOT random. In an array with keys from one to 10, where 2 random keys are picked, 0 is picked as the first number 18.8% of the time, and only as second number in 1.1% of the time:

$n=100000;

$a=array(1,2,3,4,5,6,7,8,9,10);

$b=array();

for($i=0;$i<sizeof($a);$i++) {

$b[$i]=array(0,0);

}

for($i=0;$i<$n;$i++) {

$keys=array_rand($a,2);

$b[$keys[0]][0]++;

$b[$keys[1]][1]++;

}

for ($i=0;$i<sizeof($b);$i++){

printf("%d: %04.1f%% %04.1f%% %04.1f%%", $i, ($b[$i][0]/$n*100),($b[$i][1]/$n*100),($b[$i][0]+$b[$i][1])/$n*100);

}

The result is:

0: 18.8% 01.1% 19.9%

1: 17.0% 03.3% 20.3%

2: 14.3% 05.7% 20.0%

3: 12.2% 07.9% 20.1%

4: 10.0% 10.0% 20.0%

5: 07.8% 12.0% 19.8%

6: 05.5% 14.5% 20.0%

7: 03.3% 16.6% 19.9%

8: 01.2% 18.9% 20.1%

9: 10.0% 09.9% 19.9%

The workaround is adding a shuffle command to shuffle the keys:

0: 10.0% 10.0% 20.0%

1: 10.0% 10.0% 20.0%

2: 10.0% 10.0% 20.0%

3: 10.0% 10.0% 20.0%

4: 10.0% 10.0% 20.0%

5: 10.0% 10.0% 20.0%

6: 10.1% 10.0% 20.1%

7: 10.0% 10.0% 20.0%

8: 10.0% 10.0% 20.0%

9: 10.0% 10.0% 20.0%

inVINCEable · April 19, 2009

I see, but why would the EXACT same combination of lines be coming up?

alphanumetrix · April 19, 2009

Try shuffle();

I don't really know all that much about it, but I don't think the algorithms that create the "random" results are ACTUALLY random. I think its more "complexly shuffled around", to try and simulate a random result. Because actually, I don't think ANYTHING is truly random. Not even the flip of a coin. It can be controlled under certain circumstances. Therefore, I would presume that after so long, you would receive similar/the same results if your actual count your randomizing isn't changing.

Again, just something I theorized. Don't know if it's true or not.

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array_rand, not really random... is there a better way to grab a random line?

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