Not generating the same random number twice....

[Mark]

Hi Yall

I have a page where I want 5 images to appear, randomly selected from a pool
of 50 images called 1.jpg to 50.jpg

The following code works nicely, except for one (probably obvious)
problem...

$count=1;
do {
$random = rand(1,50);
echo "<img src='images/$random.jpg'>";
$count++;
}
while ($count<5);

The problem is that there is nothing to stop images appearing more than
once. I do not want this to happen...

Any ideas on a possible solution?

TIA

Mark

[Oli Filth]

Re: Not generating the same random number twice....

Mark said the following on 13/06/2005 19:59:[color=blue]
> Hi Yall
>
> I have a page where I want 5 images to appear, randomly selected from a pool
> of 50 images called 1.jpg to 50.jpg
>
> The following code works nicely, except for one (probably obvious)
> problem...
>
> $count=1;
> do {
> $random = rand(1,50);
> echo "<img src='images/$random.jpg'>";
> $count++;
> }
> while ($count<5);
>
> The problem is that there is nothing to stop images appearing more than
> once. I do not want this to happen...
>
> Any ideas on a possible solution?
>[/color]

Set up an array of 50 Booleans, each initially FALSE. Every time a
random number is chosen, check to see if the corresponding entry in the
array is FALSE. If it is, set it to TRUE, and use that number. If it is
already TRUE, choose another random number.


--
Oli

[Chung Leong]

Re: Not generating the same random number twice....

1. Use range() to create an array with number 1 - 50.
2. Use shuttle() to shuffle the numbers.
3. Save the array in session variable.
4. Use the proper indices, depending on which page the user's is on, to
obtain 5 random numbers from the array.

[Andy Hassall]

Re: Not generating the same random number twice....

On Mon, 13 Jun 2005 19:59:25 +0100, "Mark" <mark@ilovespam .com> wrote:
[color=blue]
>I have a page where I want 5 images to appear, randomly selected from a pool
>of 50 images called 1.jpg to 50.jpg
>
>The following code works nicely, except for one (probably obvious)
>problem...
>
>The problem is that there is nothing to stop images appearing more than
>once. I do not want this to happen...
>
>Any ideas on a possible solution?[/color]

http://uk2.php.net/range

http://uk.php.net/array_rand

<?php print_r(array_r and(range(1,50) , 5)); ?>

It uses the keys rather than values so you'll probably want to add one when
making the filename.

--
Andy Hassall / <andy@andyh.co. uk> / <http://www.andyh.co.uk >
<http://www.andyhsoftwa re.co.uk/space> Space: disk usage analysis tool

[Justin Koivisto]

Re: Not generating the same random number twice....

Chung Leong <chernyshevsky@ hotmail.com> wrote:
[color=blue]
> 1. Use range() to create an array with number 1 - 50.
> 2. Use shuttle() to shuffle the numbers.[/color]

That's shuffle not shuttle. ;)
[color=blue]
> 3. Save the array in session variable.
> 4. Use the proper indices, depending on which page the user's is on, to
> obtain 5 random numbers from the array.[/color]

Why not simply use array_pop() to get through the 50 images? Then when
the array is empty, start at step one again...

Taking 5 random entries from a shuffled (random) array doesn't quite
make sense to me, or am I missing something?

--
Justin Koivisto - justin@koivi.co m

http://koivi.com

[Ewoud Dronkert]

Re: Not generating the same random number twice....

On Mon, 13 Jun 2005 19:06:29 GMT, Oli Filth wrote:[color=blue][color=green]
>> The problem is that there is nothing to stop images appearing more
>> than once. I do not want this to happen...[/color]
>
> Set up an array of 50 Booleans, each initially FALSE. Every time a
> random number is chosen, check to see if the corresponding entry in the
> array is FALSE. If it is, set it to TRUE, and use that number. If it is
> already TRUE, choose another random number.[/color]

Bad idea, generally. In this particular case, with these small numbers
and 5 rather smaller than 50, it will probably not be problematic, but
what if you're trying to generate the whole range in random order and
that darn last number just won't pop up..? Easy solution:

$a = range( 1, 50 );
$b = shuffle( $a );
for ( $i = 0; $i < 5; ++$i )
echo $b[$i]."\n";

Or written out:

$n = 50; // range 1..n
$k = 5; // 1 <= k <= n
$a = range( 1, $n );
for ( $i = 0; $i < $k; ++$i )
{
$j = mt_rand( $i, $n - 1 );
echo $a[$j]."\n";
$a[$j] = $a[$i];
}


--
Firefox Web Browser - Rediscover the web - http://getffox.com/
Thunderbird E-mail and Newsgroups - http://gettbird.com/

[Ewoud Dronkert]

Re: Not generating the same random number twice....

On Mon, 13 Jun 2005 20:33:19 +0100, Andy Hassall wrote:[color=blue]
> http://php.net/array_rand[/color]

Ah yes.


--
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[Chung Leong]

Re: Not generating the same random number twice....

I'm just guessing that the script involves paging through a list of
fifty images, five at a time. If that's case you'd need to have the
same array as you go from page to page. Otherwise then, yes, as you
said, you can just pop 5 numbers off the array.

Another way to maintain the same randomized array across pages is to
seed the random number engine with a fixed number, like today's date. A
useful trick when you don't want to use session.

[Mark]

Re: Not generating the same random number twice....

Thanks for your replies guys (n gals?)

I will try them all and let you know who was "THE CHOSEN ONE"

Thanks again!

Mark



"Mark" <mark@ilovespam .com> wrote in message
news:1118689179 .0bfe721d1be719 44ad69de19a67d3 613@teranews...[color=blue]
> Hi Yall
>
> I have a page where I want 5 images to appear, randomly selected from a
> pool of 50 images called 1.jpg to 50.jpg
>
> The following code works nicely, except for one (probably obvious)
> problem...
>
> $count=1;
> do {
> $random = rand(1,50);
> echo "<img src='images/$random.jpg'>";
> $count++;
> }
> while ($count<5);
>
> The problem is that there is nothing to stop images appearing more than
> once. I do not want this to happen...
>
> Any ideas on a possible solution?
>
> TIA
>
> Mark
>[/color]

[Dominik Susmel]

Re: Not generating the same random number twice....

- seed the rand
- put nubers in array with array_rand
- use array_unique to initialize duplicate entries with 0
- do some magic to 0 numbers in contrast to existing stuff in array

--
Dominik Susmel | art director
www.vongestern.com | vonGestern art company . Zagreb, Croatia

[Geoff Berrow]

Re: Not generating the same random number twice....

I noticed that Message-ID:
<1118689179.0bf e721d1be71944ad 69de19a67d3613@ teranews> from Mark
contained the following:
[color=blue]
>The problem is that there is nothing to stop images appearing more than
>once. I do not want this to happen...
>
>Any ideas on a possible solution?[/color]

The following picks lottery balls (6 unique balls out of 49) Trivial to
adapt it to what you want.

<html>
<body style="color:re d"><?php

for($i=1;$i<50; $i++){
$balls[]=$i;
}

for($i=0;$i<6;$ i++){
$key=array_rand ($balls);
$ballschosen[]=$balls[$key];
unset($balls[$key]);
}

asort($ballscho sen);

foreach($ballsc hosen as $choice){
print"$choice ";
}

?>
</body>
</html>

--
Geoff Berrow 011000100110110 0010000000110
001101101011011 001000110111101 100111001011
100110001101101 111001011100111 010101101011

[Shelly]

Re: Not generating the same random number twice....


<chernyshevsky@ hotmail.com> wrote in message
news:1118693141 .851760.37230@z 14g2000cwz.goog legroups.com...[color=blue]
> I'm just guessing that the script involves paging through a list of
> fifty images, five at a time. If that's case you'd need to have the
> same array as you go from page to page. Otherwise then, yes, as you
> said, you can just pop 5 numbers off the array.
>
> Another way to maintain the same randomized array across pages is to
> seed the random number engine with a fixed number, like today's date. A
> useful trick when you don't want to use session.
>[/color]

Isn't this doing double work? The shuffle randomizes the array. Then, all
you need to do is take the first five elements, since they are already in
random order. -- or am I missing something?

Shelly

[Ewoud Dronkert]

Re: Not generating the same random number twice....

On Mon, 13 Jun 2005 23:58:32 +0200, Dominik Susmel wrote:[color=blue]
> - seed the rand[/color]

Not needed as of PHP4.2.0
[color=blue]
> - put nubers in array with array_rand[/color]

That is not how array_rand() works, please see http://php.net/array-rand
[color=blue]
> - use array_unique to initialize duplicate entries with 0[/color]

Duplicate entries?! Bad algorithm. Also, that is not how array_unique()
works, please see http://php.net/array-unique
[color=blue]
> - do some magic to 0 numbers in contrast to existing stuff in array[/color]

This is really helpful.


--
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[Ewoud Dronkert]

Re: Not generating the same random number twice....

On Mon, 13 Jun 2005 23:54:08 +0100, Geoff Berrow wrote:[color=blue]
> for($i=1;$i<50; $i++){
> $balls[]=$i;
> }[/color]

See http://php.net/range
[color=blue]
> for($i=0;$i<6;$ i++){
> $key=array_rand ($balls);
> $ballschosen[]=$balls[$key];
> unset($balls[$key]);
> }[/color]

See http://php.net/shuffle
[color=blue]
> asort($ballscho sen);[/color]

Why use asort when you don't use the keys? See http://php.net/asort
[color=blue]
> foreach($ballsc hosen as $choice){
> print"$choice ";
> }[/color]



--
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Thunderbird E-mail and Newsgroups - http://gettbird.com/

[nemo]

Re: Not generating the same random number twice....

[snip]
All these much more sophisticated solutions make me wonder where I went
wrong in the early days.

while $Result etc
{
$Query="select image_filename from Tablename order by rand() limit 5";
images[]=$Row[image_filename];
}

Then position $images[0] $images[1] $images[2] where you want them.

Is there a prize for the neatest one? </pant-pant>