How to determine whether it is an indexed array in php

Example, detect whether a php array is an index array.

function is_assoc($arr){
 return array_keys($arr) !== range(0, count($arr) - 1);
 // array_values($arr) ! == $arr
}
function is_assoc2($array) {
 return (bool)count(array_filter(array_keys($array), 'is_string'));
}
$array = array(0=>"1" ,1=>"3");
var_dump($array);
echo is_assoc($array)?'Index array':'Not an index array';
echo "";
echo is_assoc2 ($array)?'Indexed array':'Not an indexed array';
echo "";

$array = array("0"=>"1","1"=> "3");
var_dump($array);
echo is_assoc($array)?'index array':'not an index array';
echo "";
echo is_assoc2($array)? 'Index array': 'Not an index array';
echo "";

$array = array("name"=>"1","age"=>"3");
var_dump($array);
echo is_assoc($array)?'index array':'not an index array';
echo "";
echo is_assoc2($array)?'index array': 'Not an indexed array';

output:

array (size=2) 0 => string '1' (length=1) 1 => string '3' (length=1) Not an indexed array Not an indexed array array (size=2) 0 => string '1' (length=1) 1 => string '3' (length=1) Not an indexed array Not an indexed array array (size=2) 'name' => string '1' (length=1) 'age' => string '3' (length=1) index array Index array