Select Random and Unique Items From a Master Array to Load to 4 Arrays

Question

Can you please let me know how I can select 20 unique items for 4 arrays from a Master Array?

I have an array called $countries which looks like

$countries = ("Afghanistan", "Albania", "Algeria", "Andorra", "Angola", "Anguilla", "Antigua & Barbuda", "Argentina", "Armenia", "Aruba", "Australia", "Austria", "Azerbaijan", "Bahamas", "Bahrain", "Bangladesh", "Barbados", "Belarus", "Belgium", "Belize", "Benin", "Bermuda", "Bhutan", "Bolivia", "Bosnia & Herzegovina", "Botswana", "Brazil", "British Virgin Islands", "Brunei", "Bulgaria", "Burkina Faso", "Burundi", "Cambodia", "Cameroon", "Cape Verde", "Cayman Islands", "Chad", "Chile", "China", "Colombia", "Congo", "Cook Islands", "Costa Rica", "Cote D Ivoire", "Croatia", "Cruise Ship", "Cuba", "Cyprus", "Czech Republic", "Denmark", "Djibouti", "Dominica", "Dominican Republic", "Ecuador", "Egypt", "El Salvador", "Equatorial Guinea", "Estonia", "Ethiopia", "Falkland Islands", "Faroe Islands", "Fiji", "Finland", "France", "French Polynesia", "French West Indies", "Gabon", "Gambia", "Georgia", "Germany", "Ghana", "Gibraltar", "Greece", "Greenland", "Grenada", "Guam", "Guatemala", "Guernsey", "Guinea", "Guinea Bissau", "Guyana", "Haiti", "Honduras", "Hong Kong", "Hungary", "Iceland", "India", "Indonesia", "Iran", "Iraq", "Ireland", "Isle of Man", "Israel", "Italy", "Jamaica", "Japan", "Jersey", "Jordan", "Kazakhstan", "Kenya", "Kuwait", "Kyrgyz Republic", "Laos", "Latvia", "Lebanon", "Lesotho", "Liberia", "Libya", "Liechtenstein", "Lithuania", "Luxembourg", "Macau", "Macedonia", "Madagascar", "Malawi", "Malaysia", "Maldives", "Mali", "Malta", "Mauritania", "Mauritius", "Mexico", "Moldova", "Monaco", "Mongolia", "Montenegro", "Montserrat", "Morocco", "Mozambique", "Namibia", "Nepal", "Netherlands", "Netherlands Antilles", "New Caledonia", "New Zealand", "Nicaragua", "Niger", "Nigeria", "Norway", "Oman", "Pakistan", "Palestine", "Panama", "Papua New Guinea", "Paraguay", "Peru", "Philippines", "Poland", "Portugal", "Puerto Rico", "Qatar", "Reunion", "Romania", "Russia", "Rwanda", "Saint Pierre & Miquelon", "Samoa", "San Marino", "Satellite", "Saudi Arabia", "Senegal", "Serbia", "Seychelles", "Sierra Leone", "Singapore", "Slovakia", "Slovenia", "South Africa", "South Korea", "Spain", "Sri Lanka", "St Kitts & Nevis", "St Lucia", "St Vincent", "St. Lucia", "Sudan", "Suriname", "Swaziland", "Sweden", "Switzerland", "Syria", "Taiwan", "Tajikistan", "Tanzania", "Thailand", "Timor L'Este", "Togo", "Tonga", "Trinidad & Tobago", "Tunisia", "Turkey", "Turkmenistan", "Turks & Caicos", "Uganda", "Ukraine", "United Arab Emirates", "United Kingdom", "Uruguay", "Uzbekistan", "Venezuela", "Vietnam", "Virgin Islands (US)", "Yemen", "Zambia", "Zimbabwe");

and I have 4 arrays like

$cat1= array();
$cat2= array();
$cat3= array();
$cat3= array();

now I would like to load 20 random and unique items into each of these 4 arrays. Can you please let me know how to do this in PHP?

Update

$cat1= array();
$rand_keys = array_rand($countries, 13);
array_push($cat1,$rand_keys);
print_r($cat1);

Answer 1

<?php
$countries = array("Afghanistan" , "Albania", "Algeria", "Andorra", "Angola", "Anguilla", "Antigua &amp; Barbuda", "Argentina", "Armenia", "Aruba", "Australia", "Austria", "Azerbaijan", "Bahamas", "Bahrain", "Bangladesh", "Barbados", "Belarus", "Belgium", "Belize", "Benin", "Bermuda", "Bhutan", "Bolivia", "Bosnia &amp; Herzegovina", "Botswana", "Brazil", "British Virgin Islands", "Brunei", "Bulgaria", "Burkina Faso", "Burundi", "Cambodia", "Cameroon", "Cape Verde", "Cayman Islands", "Chad", "Chile", "China", "Colombia", "Congo", "Cook Islands", "Costa Rica", "Cote D Ivoire", "Croatia", "Cruise Ship", "Cuba", "Cyprus", "Czech Republic", "Denmark", "Djibouti", "Dominica", "Dominican Republic", "Ecuador", "Egypt", "El Salvador", "Equatorial Guinea", "Estonia", "Ethiopia", "Falkland Islands", "Faroe Islands", "Fiji", "Finland", "France", "French Polynesia", "French West Indies", "Gabon", "Gambia", "Georgia", "Germany", "Ghana", "Gibraltar", "Greece", "Greenland", "Grenada", "Guam", "Guatemala", "Guernsey", "Guinea", "Guinea Bissau", "Guyana", "Haiti", "Honduras", "Hong Kong", "Hungary", "Iceland", "India", "Indonesia", "Iran", "Iraq", "Ireland", "Isle of Man", "Israel", "Italy", "Jamaica", "Japan", "Jersey", "Jordan", "Kazakhstan", "Kenya", "Kuwait", "Kyrgyz Republic", "Laos", "Latvia", "Lebanon", "Lesotho", "Liberia", "Libya", "Liechtenstein", "Lithuania", "Luxembourg", "Macau", "Macedonia", "Madagascar", "Malawi", "Malaysia", "Maldives", "Mali", "Malta", "Mauritania", "Mauritius", "Mexico", "Moldova", "Monaco", "Mongolia", "Montenegro", "Montserrat", "Morocco", "Mozambique", "Namibia", "Nepal", "Netherlands", "Netherlands Antilles", "New Caledonia", "New Zealand", "Nicaragua", "Niger", "Nigeria", "Norway", "Oman", "Pakistan", "Palestine", "Panama", "Papua New Guinea", "Paraguay", "Peru", "Philippines", "Poland", "Portugal", "Puerto Rico", "Qatar", "Reunion", "Romania", "Russia", "Rwanda", "Saint Pierre &amp; Miquelon", "Samoa", "San Marino", "Satellite", "Saudi Arabia", "Senegal", "Serbia", "Seychelles", "Sierra Leone", "Singapore", "Slovakia", "Slovenia", "South Africa", "South Korea", "Spain", "Sri Lanka", "St Kitts &amp; Nevis", "St Lucia", "St Vincent", "St. Lucia", "Sudan", "Suriname", "Swaziland", "Sweden", "Switzerland", "Syria", "Taiwan", "Tajikistan", "Tanzania", "Thailand", "Timor L'Este", "Togo", "Tonga", "Trinidad &amp; Tobago", "Tunisia", "Turkey", "Turkmenistan", "Turks &amp; Caicos", "Uganda", "Ukraine", "United Arab Emirates", "United Kingdom", "Uruguay", "Uzbekistan", "Venezuela", "Vietnam", "Virgin Islands (US)", "Yemen", "Zambia", "Zimbabwe");
function return_twenty_unique(&$countriesarray){
    $i = 0;
    $output = array();
    $max = 20;
    $random_keys = array_rand($countriesarray,$max);
    while($i < $max){
        $output[] = $countriesarray[$random_keys[$i]];
        unset($countriesarray[$random_keys[$i]]);
        $i++;
    }
    return $output;
}

$a1 = return_twenty_unique($countries);
$a2 = return_twenty_unique($countries);
$a3 = return_twenty_unique($countries);
$a4 = return_twenty_unique($countries);

Edit to response:
It does make more sense to use foreach loop here indeed

function return_twenty_unique(&$countriesarray){
    $output = array();
    $random_keys = array_rand($countriesarray,20);
    foreach($random_keys as $randomID){
        $output[] = $countriesarray[$randomID];
        unset($countriesarray[$randomID]);
    }
    return $output;
}

Also note that after each return_twenty_unique function call, the original $countries array will lose the 20 random values, keep this in mind if you are planning to reuse the array.

Answer 2

Try using the array_rand function, as described in the PHP docs here: array_rand

It takes an array, and some integer, and returns that many random array keys. Once you have those, put them in one of your $cat arrays, remove the keys from the master array, and repeat as necessary. I would have a temporary array to store the master values, in the meantime.

There are probably more elegant ways to do this too, but this was the first to come to mind.