PHP rand () excludes certain numbers

Question

I have it:

<?php $n = rand(1,1600); echo $n ?> 

I want to exclude from random numbers, say, 234, 1578, 763, 1274 and other numbers. How can I do it?

Answer 1

 <?php while( in_array( ($n = rand(1,1600)), array(234, 1578 ,763 , 1274) ) ); 

Answer 2

try it

 do { $n = rand(1,1600); } while(in_array($n, array(234, 1578 ,763 , 1274 )); echo $n; 

Answer 3

Check not the number you don't need if it gets a new random number.

 function getRandomNumber() { do { $n = mt_rand(1,1600); } while(in_array($n, array(234,1578, 763, 1274))); return $n; } 

Answer 4

Or avoid creating loops with random (possibly infinite) runtimes:

 /** * Returns a random integer between $min and $max (inclusive) and * excludes integers in $exarr, returns false if no such number * exists. * * $exarr is assumed to be sorted in increasing order and each * element should be unique. */ function random_exclude($min, $max, $exarr = array()) { if ($max - count($exarr) < $min) { return false; } // $pos is the position that the random number will take // of all allowed positions $pos = rand(0, $max - $min - count($exarr)); // $num being the random number $num = $min; // while $pos > 0, step to the next position // and decrease if the next position is available for ($i = 0; $i < count($exarr); $i += 1) { // if $num is on an excluded position, skip it if ($num == $exarr[$i]) { $num += 1; continue; } $dif = $exarr[$i] - $num; // if the position is after the next excluded number, // go to the next excluded number if ($pos >= $dif) { $num += $dif; // -1 because we're now at an excluded position $pos -= $dif - 1; } else { // otherwise, return the free position return $num + $pos; } } // return the number plus the open positions we still had to go return $num + $pos; } 

This function selects a random position and passes an array of exceptions to find a free position. Opening hours depend on the number of rooms to be excluded. If you want to exclude certain ranges, you can adapt the algorithm to take this into account.

Answer 5

Always use cryptographically robust algorithms to generate random numbers:

 /** * @param int $from From number * @param int $to To number * @param array $excluded Additionally exclude numbers * @return int */ function randomNumber($from, $to, array $excluded = []) { $func = function_exists('random_int') ? 'random_int' : 'mt_rand'; do { $number = $func($from, $to); } while (in_array($number, $excluded, true)); return $number; } var_dump(randomNumber(1, 100)); var_dump(randomNumber(1, 10, [5, 6, 7, 8])); var_dump(randomNumber(1, 100, range(10, 90))); 

I would also recommend using the paragonie / random_compat library for compatibility when using multiple versions of PHP.

Answer 6

You can create an array with real numbers.

Then your random number generation should return an index into this array.

Answer 7

If you have too many numbers to exclude, it’s easier and faster to just try again if you find an unwanted number:

 $n = 0; while (in_array($n, array(0, 234, 1578 ,763 , 1274))) { $n = rand(1,1600); } echo $n; 

Answer 8

Another solution for this may be as follows:

 function random_number($min, $max, $exclude) { $number = rand($min, $max); if(in_array($number, $exclude)) { random_number($min, $max, $exclude); } else { return $number; } } $number = random_number(1,10, [2,5,6]); 

Answer 9

As the volume of blacklisted integers approaches the size of the whole range of integers, it becomes more and more convincing to listen to @regenschein's advice.

A non-iterative approach might look like this:

 $range = range(1, 1600); $blacklist = [234, 1578, 763, 1274]; // 4 blacklisted versus 1600 full range is NOT compelling $valids = array_diff($range, $blacklist); echo array_values($valids)[rand(0, count($valids) - 1)]; // or echo $valids[array_rand($valids)]; // the two approaches use different randomizers 

Or, if you are just as happy, you can do:

 $blacklist = [234, 1578, 763, 1274]; $range = range(1, 1600); $valids = array_diff($range, $blacklist); shuffle($valids); echo $valids[0]; 

* Please note that array_diff() especially array_diff() if you want to pass multiple arrays of blacklist - just separate them with commas.

For instance:

 var_export($valids = array_diff(range(1, 100), range(5, 50), range(61, 99), [55])); 

Output:

 array ( 0 => 1, 1 => 2, 2 => 3, 3 => 4, 50 => 51, 51 => 52, 52 => 53, 53 => 54, 55 => 56, 56 => 57, 57 => 58, 58 => 59, 59 => 60, 99 => 100, ) 

Answer 10

I know this is a bit outdated, but I think the operation is trying to shuffle integers. If so, then the following method is better

 $array = array(1,2,3,4,5,6,7); shuffle($array); 

This code randomizes the order of the exact elements of the array without repeating and returns the result inside the array itself.