Getting the right index

Here's a DataFrame named matches containing potential matches between two DataFrames, users_1 and users_2. Each DataFrame's row indices is stored in uid_1 and uid_2 respectively.

             first_name  address_1  address_2  marriage_status  date_of_birth
uid_1 uid_2
0     3              1          1          1                1              0
...            ...         ...        ...              ...            ...
...            ...         ...        ...              ...            ...
1     3              1          1          1                1              0
...            ...         ...        ...              ...            ...
...            ...         ...        ...              ...            ...


How do you extract all values of the uid_1 index column?