Finds an order corresponding to an entry within the sequence.
| Parameter | Description | Default Value | 
| Cntnr | Container type. | - | 
| Type | Definition | Description | 
| order_statistics_key_type | typename Cntnr::key_type | Order-statistics key type. | 
| underlying_key_type | typename order_statistics_key_type::key_type | Underlying key type. | 
| Type | Definition | Description | 
| cntnr | Cntnr | Container type. | 
| size_type | typename cntnr::size_type | Container's size type. | 
| Method | Description | 
| inline size_type operator() (const Cntnr &r_c, const underlying_key_type &r_key) const | Returns the order of a key within a sequence. For exapmle, if r_key is the smallest key in r_c, this method will return 0; if r_key is a key between the smallest and next key in r_c, this method will return 1; if r_key is a key larger than the largest key in r_c, this method will return the size of r_c. |