Select Two Unique Random From Array while Are not Equal to a Given Value

Question

How can I select two unique random from and array and check that it are not equal with one pre-selected (default value)? For example I have an array of months like

 $months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun","Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];

and a given month $alreadyin = "Feb"; now I need to select two unique months which are not equal to $alreadyin?

<?php
    $alreadyin = "Feb";
    $months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun","Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
    $rand_months = array_rand($months, 2);
?>

compare $rand_months with $alreadyin. If it's in, do array rand again. You can put it in a while loop that only exits when two uniques are generated. — Ibu
– Ibu, Commented Dec 18, 2018 at 19:49

AbraCadaver · Accepted Answer · 2018-12-18 20:12:09Z

4

Compute the difference (get months that are not $alreadyin) and then select 2 at random:

$rand_months = array_rand(array_diff($months, [$alreadyin]), 2);

You could also search for and remove $alreadyin:

unset($months[array_search($alreadyin, $months)]);
$rand_months = array_rand($months, 2);

array_rand returns random keys from the array, so you may need something like:

foreach($rand_months as $key) {
    echo $months[$key];
}

To get the actual month names using the first example, shuffle the array and slice 2:

$months = array_diff($months, [$alreadyin]);
shuffle($months);
$rand_months = array_slice($months, 0, 2);

Or using the second example:

unset($months[array_search($alreadyin, $months)]);
shuffle($months);
$rand_months = array_slice($months, 0, 2);

edited Dec 18, 2018 at 20:12

answered Dec 18, 2018 at 19:54

AbraCadaver

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4 Comments

Mona Coder Over a year ago

Thanks Abra but why I am getting associated array instead of name of months?

AbraCadaver Over a year ago

Because array_rand returns the keys, I was just using what you had.

ggorlen Over a year ago

Great answer. array_rand() returns random indices. You'll need to add a final step to index into the original array using each of the returned indices like

$rand_months = array_map(function ($e) use ($months) {     return $months[$e]; }, array_rand(array_diff($months, [$alreadyin]), 2));

Mona Coder Over a year ago

but the output looks like [0] => 3 [1] => 8 instead of [0] => Mar [1] => Aug

Ibu · Accepted Answer · 2018-12-18 19:54:42Z

0

You can use this simple process. Get random values, check if they match, repeat if they don't.

function getUniqueMonth( $alreadyin ) {
    $months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun","Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];

    while( true ) {
        $rand_months = array_rand( $months, 2 );
        if ( !in_array( $alreadyin, $rand_months ) ) {
            return $rand_months;
        }
    }
}

You can always add a counter for safety, to make sure the computer doesn't keep looping forever.

answered Dec 18, 2018 at 19:54

Ibu

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