Find highest value in multidimensional array

Just do a simple loop and compare values or use array_reduce. @ is an error suppressor; it hides the fact that $a['total'] is not declared before it is accessed on the first iteration. Demo

$data = array_reduce($data, function ($a, $b) {
    return @$a['Total'] > $b['Total'] ? $a : $b ;
});

print_r($data);
// Array( [Key2] => Key2 [Total] => 117 )

---

It could also be written with arrow function syntax which has been avaiable since PHP7.4. Demo

var_export(
    array_reduce(
        $data,
        fn($result, $row) =>
            $result['Total'] > $row['Total']
            ? $result
            : $row,
        ['Key1' => null, 'Total' => PHP_INT_MIN]
    )
);
// array ('Key2' => 'Key2', 'Total' => 117,)

I know this question is old, but I'm providing the following answer in response to another question that pointed here after being marked as a duplicate. This is another alternative I don't see mentioned in the current answers.

I know there's a function called max but that doesn't work with a multidimensional array like this.

You can get around that with array_column which makes getting the maximum value very easy:

$arr = [['message_id' => 1,
             'points' => 3],
        ['message_id' => 2,
             'points' => 2],
        ['message_id' => 3,
             'points' => 2]];

// max value
$max = max(array_column($arr, 'points'));

Getting the associative key is where it gets a little more tricky, considering that you might actually want multiple keys (if $max matches more than one value). You can do this with an anonymous function inside array_map, and use array_filter to remove the null values:

// keys of max value
$keys = array_filter(array_map(function ($arr) use ($max) {
    return $arr['points'] == $max ? $arr['message_id'] : null;
}, $arr));

Output:

array(1) {
  [0]=>
  int(1)
}

If you do end up with multiples keys but are only interested in the first match found, then simply reference $keys[0].

Since PHP 5.5 you can use array_column to get an array of values for specific key, and max it.

max(array_column($array, 'Total'))

It's so basic algorithm.

$max = -9999999; //will hold max val
$found_item = null; //will hold item with max val;

foreach($arr as $k=>$v)
{
    if($v['Total']>$max)
    {
       $max = $v['Total'];
       $found_item = $v;
    }
}

echo "max value is $max";
print_r($found_item);

Working demo