random value based on timestamp

[myphptrip]

hi there, I'm using this function to get a random value from an array every new full hour.

function RandomQuoteByInterval($TimeBase, $QuotesArray){
 
    // Make sure it is a integer
    $TimeBase = intval($TimeBase);
 
    // How many items are in the array?
    $ItemCount = count($QuotesArray);
 
    // By using the modulus operator we get a pseudo
    // random index position that is between zero and the
    // maximal value (ItemCount)
    $RandomIndexPos = ($TimeBase % $ItemCount);
 
    // Now return the random array element
    return $QuotesArray[$RandomIndexPos];

it's initiated via something like this:

$DayOfTheYear = date('h'); 
 
// Example array with some random quotes
$RandomQuotes = array(
    'No animals were harmed in the making of this snippet.',
    'Nice snippets',
    'The modulus operator rocks!',
    'PHP is cool.'
);
 
print RandomQuoteByInterval($DayOfTheYear, $RandomQuotes);
 

Is my assumption correct that this will return the same value for let's say 3pm every day? because as far as I can read it, the randomness is defined only by the number of the hour.

 

If so, I am looking for a way that will change it. I don't want to return the same value that is returned on 3pm everyday. I want it to be random at the hour - but not constant across days.

 

I guess I could achieve it by adding day month and year value to the $RandomIndexPos?

$currentYear = date('Y'); 
$currentMonth = date('m'); 
$currentDay = date('d'); 

$RandomIndexPos = ($TimeBase % $ItemCount) + $currentYear +$currentMonth + $currentDay;

Would it work?

 

[requinix]

Is my assumption correct that this will return the same value for let's say 3pm every day? because as far as I can read it, the randomness is defined only by the number of the hour.

Correct. And it's not random: it cycles through each quote in order... with a limit of 12 quotes because the 'h' value has a range of 1-12.

 

If so, I am looking for a way that will change it. I don't want to return the same value that is returned on 3pm everyday. I want it to be random at the hour - but not constant across days.

 

I guess I could achieve it by adding day month and year value to the $RandomIndexPos?

$currentYear = date('Y'); 
$currentMonth = date('m'); 
$currentDay = date('d'); 

$RandomIndexPos = ($TimeBase % $ItemCount) + $currentYear +$currentMonth + $currentDay;

Would it work?

 

Almost. You have to do the modulus (%) on the total number, not on just the $TimeBase.

$RandomIndexPos = ($TimeBase + $currentYear + $currentMonth + $currentDay) % $ItemCount;

However, you don't have to do it in RandomQuoteByInterval. In fact I would not. Just call the function with the new number.

 

And while I'm in the code, here's another way of getting the random result:

$TimeValue = floor(time() / 3600); // number of hours since Jan 1 1970
 
// Example array with some random quotes
$RandomQuotes = array(
    'No animals were harmed in the making of this snippet.',
    'Nice snippets',
    'The modulus operator rocks!',
    'PHP is cool.'
);
 
print RandomQuoteByInterval($TimeValue, $RandomQuotes);

As before this is not random: it will cycle through quotes in order. If you wanted it in "truly" random order then you'd need different code...

[myphptrip]

 

As before this is not random: it will cycle through quotes in order. If you wanted it in "truly" random order then you'd need different code...

 

 

 

thank you!

$TimeValue = floor(time() / 3600); // number of hours since Jan 1 1970

makes more sense, yeah.

 

yeah it isn't that random - you can (obviously) calculate it.

since there are 50 items in the array I am actually using, it shouldn't matter I guess.

 

on the other hand: couldn't I just shuffle the array before itemcount kicks in?

[requinix]

Not really: shuffle() is random so you'd end up with a different quote every time. You'd need something more than that. The standard way to deal with this is to use PHP's random number generators (rand(), mt_rand()) but seeding, the way you could get a set of stable random results, isn't reliable anymore: srand() is disabled if PHP is installed with the Suhosin patch/extension and that's popular with shared hosting environments, while mt_srand() won't guarantee the stability because of what it can do to the seed number.

 

A sort of pseudo-random shuffle would be fine: shuffle the items in the array so that quote #N doesn't always appear before quote #N+1. Something like

function RandomQuoteByInterval($TimeBase, $QuotesArray){
 
    // Make sure it is a integer
    $TimeBase = intval($TimeBase);
 
    // How many items are in the array?
    $ItemCount = count($QuotesArray);

    // Shuffle the array in a way that looks random
    // 1. Create an array of random strings for each quote
    $QuotesKeys = array();
    foreach ($QuotesArray as $N => $Quote) {
        $QuotesKeys[$N] = md5($TimeBase . $Quote);
    }
    // 2. Sort the keys array normally, and at the same time
    // rearrange the quotes to match
    array_multisort($QuotesKeys, $QuotesArray);
 
    // By using the modulus operator we get a pseudo
    // random index position that is between zero and the
    // maximal value (ItemCount)
    $RandomIndexPos = ($TimeBase % $ItemCount);
 
    // Now return the random array element
    return $QuotesArray[$RandomIndexPos];

}

The downside to using randomness is that a particular quote may show up twice (or more) in a row. There are ways to avoid that...