random without replacement

[windandwaves]

Hi Folk

I want a random list of numbers between 0 and 58 where each number can only
occur once. I have written this ($f is an array):

for($i = 0; $i < 13; $i++) {
$rand[$i] = mt_rand(0,count ($f));
}

what else do I need?

TIA
[color=blue]
> Nicolaas[/color]

[windandwaves]

Re: random without replacement

windandwaves wrote:[color=blue]
> Hi Folk
>
> I want a random list of numbers between 0 and 58 where each number
> can only occur once. I have written this ($f is an array):
>
> for($i = 0; $i < 13; $i++) {
> $rand[$i] = mt_rand(0,count ($f));
> }
>
> what else do I need?
>
> TIA
>[color=green]
>> Nicolaas[/color][/color]

This is what I came up with:

for($i = 0; $i < 12; $i++) {
$r[$i] = mt_rand(0,count ($f));
for($j = ($i - 1); $j > -1; $j--) {
if($r[$j] == $r[$i]) {
$i = 0;
}
}
}
but it does not seem to work

Any suggestions?

TIA
[color=blue]
> Nicolaas[/color]

[yxod]

Re: random without replacement

a simple word of advice: Do not use variable names that are the same
with php functions. If at any point you forget the $, strange things
will happen. check out rand().

and now that I am on it:

// function that generates a random number that does not exists in an
array
function get_random_numb er($random_arra y) {
$random_number= mt_rand(0,58);

if(is_array($ra ndom_array)&&in _array($random_ number,$random_ array)) {
return get_random_numb er($random_arra y); // recursiveness
} else {
return $random_number;
}
}

// fill the array
for($i=0; $i<13; $i++) {
$random_array[$i]=get_random_num ber($random_arr ay);
}

// just to showcase
foreach($random _array as $number) {
echo $number.'<br>';
}

[Kimmo Laine]

Re: random without replacement

"windandwav es" <winandwaves@co ldmail.com> wrote in message
news:qFRRf.6343 $JZ1.201628@new s.xtra.co.nz...[color=blue]
> Hi Folk
>
> I want a random list of numbers between 0 and 58 where each number can
> only occur once. I have written this ($f is an array):
>
> for($i = 0; $i < 13; $i++) {
> $rand[$i] = mt_rand(0,count ($f));
> }
>
> what else do I need?[/color]

$randomstuff = range(0,58);
shuffle($random stuff);

print_r($random stuff);

--
"En ole paha ihminen, mutta omenat ovat elinkeinoni." -Perttu Sirviö
spam@outolempi. net | Gedoon-S @ IRCnet | rot13(xvzzb@bhg byrzcv.arg)

[Tyxod]

Re: random without replacement

The "shuffle" thing does the work but produces an array with 58
elements. And it works a lot faster than the recursive thing (it
matters if the function is used more than a few times in a script).

But if you need just 13 (or anything else <>58) items in the array the
recursive function is really the only sane way to go.

(of course one could "shuffle($rando mstuff);" and then pick up the
first 13 items from the resulted array, but I really dont like doing
that)

[Mladen Gogala]

Re: random without replacement

On Wed, 15 Mar 2006 23:05:09 +1300, windandwaves wrote:
[color=blue]
> I want a random list of numbers between 0 and 58 where each number can only
> occur once. I have written this ($f is an array):[/color]

You should use shuffle() function. Are you trying to win powerball?

--

http://www.mgogala.com

[Jerry Stuckle]

Re: random without replacement

Tyxod wrote:[color=blue]
> The "shuffle" thing does the work but produces an array with 58
> elements. And it works a lot faster than the recursive thing (it
> matters if the function is used more than a few times in a script).
>
> But if you need just 13 (or anything else <>58) items in the array the
> recursive function is really the only sane way to go.
>
> (of course one could "shuffle($rando mstuff);" and then pick up the
> first 13 items from the resulted array, but I really dont like doing
> that)
>[/color]

Why not?

1. It's much clearer than the recursive code
2. It's faster than the recursive code

If course - it does use 156 more bytes than the recursive solution. But
the parser will probably need more than this just to handle the extra
code anyway.

Sometimes saving a few bytes just isn't worth it!

--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attgl obal.net
=============== ===

[Tyxod]

Re: random without replacement

When I say that "I really dont like doing that", I mean that I really
don't LIKE that! :) It has nothing to do with the semantics of it, and
I agree with any other solution that worx, but I do not enjoy coding
like that. That's just me...

[Kimmo Laine]

Re: random without replacement

"Tyxod" <yrizos@gmail.c om> wrote in message
news:1142426997 .598055.231730@ j52g2000cwj.goo glegroups.com.. .[color=blue]
> When I say that "I really dont like doing that", I mean that I really
> don't LIKE that! :) It has nothing to do with the semantics of it, and
> I agree with any other solution that worx, but I do not enjoy coding
> like that. That's just me...[/color]

Well, I'm different. I don't like to "reinvent the wheel" every time I code
something, if such functionality already exists in the function library, I
use it rather than rewrite the whole thing.

As for the list being 58 elements instead of just 13, it can be easily
truncated to that using array_slice($ra ndomstuff,-13) after the shuffle() so
that ain't no problem either.

It's just that it took me a minute or two to come up with the range and
shuffle solution, while writing the recursive function would mean a lot more
work. I like to keep it neat and tidy, short and simple. Good old KISS and
LOVE rules apply, Keep It Simple, Stupid and Leave Out Virtually Everything.

--
"En ole paha ihminen, mutta omenat ovat elinkeinoni." -Perttu Sirviö
spam@outolempi. net | Gedoon-S @ IRCnet | rot13(xvzzb@bhg byrzcv.arg)

[Tyxod]

Re: random without replacement

yeap, true, but there's no fun in that...

[d]

Re: random without replacement

"Tyxod" <yrizos@gmail.c om> wrote in message
news:1142429214 .729790.27680@u 72g2000cwu.goog legroups.com...[color=blue]
> yeap, true, but there's no fun in that...[/color]

php is about efficiency first, fun second :) It's hard to have fun with a
project that has more wires than R2D2 having sex with C3P0 in a ransacked
circuit city - when it breaks, the fun quickly turns to abject horror ;)

Best practices are called best practices for a reason...

dave

[sid.bachtiar@gmail.com]

Re: random without replacement

> yeap, true, but there's no fun in that...

What's so fun about re-inventing the wheel? :-\

[windandwaves]

Re: random without replacement

Mladen Gogala wrote:[color=blue]
> On Wed, 15 Mar 2006 23:05:09 +1300, windandwaves wrote:
>[color=green]
>> I want a random list of numbers between 0 and 58 where each number
>> can only occur once. I have written this ($f is an array):[/color]
>
> You should use shuffle() function. Are you trying to win powerball?[/color]

Not sure about the powerball thing. But this is how I did it in the end:

function randomizer($arr ay, $itemsneeded) {
$r = array_rand($arr ay, $itemsneeded);
foreach($r as $c) {
$v[$c] = $array[$c];
}
return $v;
}

[Geoff Berrow]

Re: random without replacement

Message-ID: <qFRRf.6343$JZ1 .201628@news.xt ra.co.nz> from windandwaves
contained the following:
[color=blue]
>
>I want a random list of numbers between 0 and 58 where each number can only
>occur once. I have written this ($f is an array):
>
>for($i = 0; $i < 13; $i++) {
> $rand[$i] = mt_rand(0,count ($f));
>}
>
>what else do I need?[/color]

Here is my lottery ball picker

<?php
asort($rand_key s = array_rand(arra y_fill(1, 49,''), 6));
print "Your Lotto Numbers are: <big>".implode( $rand_keys,", ")."</big>";
?>

--
Geoff Berrow (put thecat out to email)
It's only Usenet, no one dies.
My opinions, not the committee's, mine.
Simple RFDs http://www.ckdog.co.uk/rfdmaker/

[Jim Carlock]

Re: random without replacement

<sid.bachtiar@g mail.com> wrote[color=blue]
> What's so fun about re-inventing the wheel? :-\[/color]

Perhaps you end up with a better wheel? Less friction? More MPG?

Perhaps you end up with no wheels at all and everything slides or
hovers along?

There's a lot of fun in reinventing the wheel. And an opportunity to
make something better.

Wheels work with friction. Lessen the friction and you end up with a
better wheel... and perhaps no braking mechanism! That in turn leads
to more revenue because the brakes require reinvention.

Jim Carlock
Reinvent the car.
Less than 3 years of oil left inside the United States Oil Reserves.
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