在数组中搜索唯一元素的算法？

Question

Which algorithm to use for searching unique element in array?

For example array is:

$arr = [
   ["date" => "2015/04/05",
   "country" => "UK",
   "number" => 3],

   ["date" => "2015/04/05",
   "country" => "UK",
   "number" => 3],

   ["date" => "2015/04/05",
    "country" => "UK",
   "number" => 3],

   ["date" => "2015/04/05",
    "country" => "UK",
   "number" => 4],

];

So, I need to count how much element with unique number?

In result I should get the following structure:

["UK" => array("total" => "2")]

Where total is number of unique number in array.

I tried as:

$output = [];

foreach ($arr as $k => $value) {

            $output[
                $value[
                    "country"
                ]][$value["date"]][$value["number"]
            ] = true;
        }

        foreach ($output as $k => $v) {

            foreach ($v as $c => $t) {

                $arr[$k][$c] = count($t);
            }
        }

But this code looks so awful, with loops. Also I think there is a trivial algorithm to resolve such issues.

Answer 1

$arr = [
   ["date" => "2015/04/05", "country" => "UK", "number" => 3],
   ["date" => "2015/04/05", "country" => "UK", "number" => 3],
   ["date" => "2015/04/05", "country" => "UK", "number" => 3],
   ["date" => "2015/04/05", "country" => "UK", "number" => 4],
];

$result=array();
foreach($arr as $value)
{
    $result[$value["country"]][$value['number']] = 1;
}

foreach ($result as $country => $a) {
    $answer[$country]['total'] = count($a);
}

print_r($answer);

Result:

Array
(
    [UK] => Array
        (
            [total] => 2
        )

)