Generating random numbers without repeats

Question

I'm building a website that will randomly display a yelp listing each time the page is refreshed. The yelp search api returns 20 listings in an array. Right now, I am using PHP's function rand(0,19) to generate a random listing every time the page is refreshed ( $businesses[rand(0,19)] ).

Can someone refer me to a smarter method to randomize? I want to show all 20 listings once before any of them are repeated. What is the preferred method to handle this problem?

the below answer doesn't work because the numbers are recreated every time I refresh the page. I'm guessing I need to store which numbers I've used already?

$numbers = range(0, 19);

shuffle($numbers);

// Handle Yelp response data
$response = json_decode($data);
$RANDOM = rand(1,19);
$business = $response->businesses;

echo "<img border=0 src='".$business[$RANDOM]->image_url."'><br/>";
echo $business[$RANDOM]->name."<br/>";
echo "<img border=0 src='".$business[$RANDOM]->rating_img_url_large."'><br/>";

?>

The easiest way to do this is pre-populate a list of sanitized random values before hand. Why wouldn't you just create the order, in advance, and pick the last one that hadn't been displayed. To casual users, this will appear to be random. — Brian Hoover
– Brian Hoover, Commented Jul 22, 2013 at 1:37
how do you keep all 20 around to show them? do you store the listings locally, or does the api send you the same ones on request? — Sheriff_McLawDog
– Sheriff_McLawDog, Commented Jul 22, 2013 at 1:38
Look up 'Fisher Yates', or see stackoverflow.com/questions/8116872/…. — paxdiablo
– paxdiablo, Commented Jul 22, 2013 at 1:38
@Sheriff_McLawDog I currently am not storing any listings. The api sends 20 listings in an array called $businesses. I want to display one listing at a time per refresh — ryank
– ryank, Commented Jul 22, 2013 at 1:56

Community · Accepted Answer · 2020-06-20 09:12:55Z

42

Easiest solution:

$numbers = range(1, 20);
shuffle($numbers);

Alternative:

<?php

function randomGen($min, $max, $quantity) {
    $numbers = range($min, $max);
    shuffle($numbers);
    return array_slice($numbers, 0, $quantity);
}

print_r(randomGen(0,20,20)); //generates 20 unique random numbers

?>

2 Comments

ryank Over a year ago

Sorry, I should have included code for better clarification. Please look at my Edit

Blackwolf Over a year ago

This is a very simple, but very clever method of getting a quantity of unique random numbers 😎

Mehul Velani · Accepted Answer · 2020-08-19 13:24:26Z

2

try this code

$a = range(1,36);

shuffle($a);

$array = array_slice($a, 0, 3);

print_r($array);

answered Aug 19, 2020 at 13:24

Mehul Velani

76110 silver badges14 bronze badges

Comments

Ali Zamani · Accepted Answer · 2024-07-31 03:40:57Z

0

You can use microtime and rand together

echo rand(11111,99999).substr(round(microtime(true) * 1000),6);

answered Jul 31, 2024 at 3:40

Ali Zamani

193 bronze badges

Comments

CPHPython · Accepted Answer · 2018-09-14 10:31:07Z

-2

I would try this via while loop:

<?php

  $i = 0;
  $arr = array();

  while($i<10){
    $num = rand(1, 12);
    $c = 0;
    echo $num . "<br>";

    for($j=0; $j<4; $j++){
      if($arr[$j] == $num){
        $c++;
        break;
      }
    }
    if($c==0){
      $arr[$i] = $num;
      $i++;
    }
  }

  echo "<pre>";
  print_r($arr);
  echo "</pre>";

edited Sep 14, 2018 at 10:31

CPHPython

13.9k5 gold badges68 silver badges77 bronze badges

answered Sep 14, 2018 at 9:49

Gazi Anis

12 bronze badges

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