Associative arrays in php
===

I have written the following code to check whether an array is associative or not

    
	function is_associative( $arr ) {
	    $arr = array_keys( $arr );
        return $arr != array_keys( $arr );
	}

It returns true for arrays like
    
    array("a" => 5,"b" => 9);
and false for numeric arrays

But it doesn't return true for associative arrays with single element like
     
    array("a" =>9);
Why does it returns false for associative arrays with single element?