Get the keys for duplicate values in an array

Question

I have the following array:

$myarray = Array(\"2011-06-21\", \"2011-06-22\", \"2011-06-22\", \"2011-06-23\", \"2011-06-23\", \"2011-06-24\", \"2011-06-24\",         


        

Answer 1

Another example:

$array = array(
  'a',
  'a',
  'b',
  'b',
  'b'
);
echo '
Array: ';
print_r($array);
// Unique values
$unique = array_unique($array);
echo '
Unique Values: ';
print_r($unique);
// Duplicates
$duplicates = array_diff_assoc($array, $unique);
echo '
Duplicates: ';
print_r($duplicates);
// Get duplicate keys
$duplicate_values = array_values(array_intersect($array, $duplicates));
echo '
duplicate values: ';
print_r($duplicate_values);

Output:

Array :Array ( [0] => a [1] => a [2] => b [3] => b [4] => b ) 
Unique Values :Array ( [0] => a [2] => b ) 
Duplicates :Array ( [1] => a [3] => b [4] => b ) 
Duplicate Values :Array ( [0] => a [1] => a [2] => b [3] => b [4] => b )