Get random from one PHP array but not match from another

Question

I have two arrays in PHP: big and small. All the values in small arrays are included in big array. I need to get random value from big array but it will be not matched with any value of small array. Something like:

$big = array('2','3','5','7','10');
$small = array('2','5','10');
$random = '3'; // it's not 2, 5 or 10

stackoverflow.com/questions/16327137/… How about removing the small array from the big array and picking a random value from the resulting items? — tbddeveloper
– tbddeveloper, Commented Jul 30, 2014 at 19:23

raidenace · Accepted Answer · 2014-07-31 07:26:23Z

3

$big = array('2','3','5','7','10');
$small = array('2','5','10');

$nums = array_diff($big,$small);//numbers in big that are not in small
$rand = array_rand($nums); //get a random key from that set
$val = $nums[$rand]; //get the value associated with that random key

edited Jul 31, 2014 at 7:26

answered Jul 30, 2014 at 19:31

raidenace

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4 Comments

dognose Over a year ago

"min/max" will work on the values, not on the keys. so, this will return a random between 3 and 7 - which is not what op wants, cause for instance "6" is possible but not part of any array.

user3892905 Over a year ago

Yes, @dognose is right, solution by raidenace doesn't work if $big = array('7','2','10','5','3'); i.e. digits of array has random order

raidenace Over a year ago

@user3892905 - array_rand returns a random key from the array. In order to get the value you have to query using that random key like : $nums[$rand]. It doesnt have anything to do with random order of digits. I have updated answer just for clarity

dognose Over a year ago

for further reader: My prior comment refered to the first version of the post which has been updated.

Rodrigo · Accepted Answer · 2014-07-30 19:31:34Z

0

$bigs = ['1', '2', '3', '5', '10'];
    $small = ['1', '5', '10'];

    foreach($bigs as $big)
    {
        if(!in_array($big, $small))
        {
            echo $big. "\n";
        }
    }

answered Jul 30, 2014 at 19:31

Rodrigo

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3 Comments

I wrestled a bear once. Over a year ago

this just echos all the unique array values. also, under normal circumstances, \n will not break the line unless you send plaintext headers to the browser.

Rodrigo Over a year ago

i just echoed it out so he could see the values being returned, I wouldn't actually return it like this @Adelphia

Marc B Over a year ago

this is basically just a more complicated array_diff() anyways.

dognose · Accepted Answer · 2014-07-30 21:54:06Z

-1

You can use array_diff() to determine the difference - and pick a random number (using mt_rand()) from the resulting array:

$arrDiff = array_values(array_diff($big, $small));
$random = $arrDiff[mt_rand(0, count($arrDiff)-1)];

Note: the array_values() method makes sure that only the values are copied to the array $arrDiff, so the indexes from 0...n-1 are filled with values.array_diff() will maintain the index-positions, so there might be no index 0, 1 or whatever, as stated by @Undefined-Variable.

edited Jul 30, 2014 at 21:54

answered Jul 30, 2014 at 19:31

dognose

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3 Comments

raidenace Over a year ago

Is there a function called random() ?

Undefined Variable Over a year ago

There is an error in your answer - array_diff retains the key original key indices - thus if you randomly select a key index between 0 and count, it might not exist.

dognose Over a year ago

@UndefinedVariable valid point. Added array_values to fix that.

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