Find element inside a PHP array, with grouping of numbers - php

Question

I have a long multi-dimensional array, with groups of numbers counting up to 100 ... For example:
$list = (
array('1-4','first'),
array('5-7','next'),
array('8-10','third group'),
array('11-12','another group'),
/* ... keep going up to 100 */
array('94-97','almost done'),
array('98-100','first')
);
I have a randomly generated number, to figure out with line to output:
$num = rand(1,100);
I'd like to know how I would go about getting the # associated inside the array. So, if I rolled a 3, I could get the first array key (1-4), and be able to print out "first" .... or if I rolled a 97, I would get the 2nd-to-last key for "almost done" (94-97). Is there a quick way to do this?
Thanks

Answer 1

You could do something like this if the structure of $list is guaranteed:
$randomRoll = rand(1,100);
array_walk($list, function($ar) use ($randomRoll){
$nums = explode('-', $ar[0]);
(int) $lower = $nums[0];
(int) $upper = $nums[1];
if (($randomRoll >= $lower) && ($randomRoll <= $upper))
{
print($ar[1]);
}
});

Answer 2

You can simplify your lookup array into an associative one since there are no gaps from 1 to 100. In other words, every random number will fall into one of the known groups by determining the greatest number that it is less than or equal to.
Don't use any functional iterators (e.g. array_filter() or array_walk()) because they will unconditionally iterate the entire lookup array. Instead, use foreach() and break as soon as possible -- this is most efficient.
Code: (Demo)
$list = [
4 => 'first', // 1 - 4
7 => 'next', // 5 = 7
10 => 'third group', // 8 - 10
12 => 'another group', // 11, 12
95 => 'huge chunk', // 13 - 95
97 => 'almost done', // 96, 97
100 => 'first' // 98 - 100
];
$num = rand(1, 100);
foreach ($list as $key => $group) {
// echo "$num vs $key\n";
if ($num <= $key) {
break; // don't iterate anymore after finding group
}
}
echo "Num = $num, Group = $group";

Answer 3

I did the following... and it seems to work. If anyone has advice on cleaning up the code, let me know... Thanks...
$dieroll = rand(1,100); // Final Roll
$numarr = array(); $j=0;
foreach ($list as $k => $v) {
$strTr = $v[0];
$nums2arr = explode("-", $strTr);
for($i=$nums2arr[0]; $i<=$nums2arr[1]; $i++) {
$numarr[] = $j;
}
$j++;
}
$roll = $list[$numarr[$dieroll-1]][1];

Answer 4

This solution uses array_filter. The result is again a 2-dimensional array with the elements that fulfill the condition of the filter function.
$filter = function($a) use($find){
list($low,$up) = explode('-',$a[0]);
return $find >= $low AND $find <= $up;
};
$arr = array_filter($list, $filter);
full example:
$list = [
['1-4','first'],
['5-7','next'],
['8-10','third group'],
['11-12','another group'],
/* ... keep going up to 100 */
['94-97','almost done'],
['98-100','first']
];
//for a test is better to use a fix number
$find = 9;
$filter = function($a) use($find){
list($low,$up) = explode('-',$a[0]);
return $find >= $low AND $find <= $up;
};
$arr = array_filter($list, $filter);
echo 'Label: '.reset($arr)[1]."<br>\n";
echo 'Area: '.reset($arr)[0]."<br>\n";
echo 'Array-Key: '.key($arr)."<br>\n";
Output:
Label: third group
Area: 8-10
Array-Key: 2
As of PHP 8.0, solutions with match are also possible for this:
$num = rand(1, 100);
$group = match(true) {
$num <= 4 => 'first',
$num <= 7 => 'next',
$num <= 10 => 'third group',
$num <= 12 => 'another group',
$num <= 95 => 'huge chunk',
$num <= 97 => 'amost done',
$num <= 100 => 'first',
};
echo "Num = $num, Group = $group";