help group_id                                                 dialog:  group_id
-------------------------------------------------------------------------------

Title

    group_id -- Groups identifiers when values for specified variables match


Syntax

        group_id id_var , matchby(match_vars)


Description

    group_id consolidates values of identifier variable id_var when
    observations are matched by match_vars. When a match is found between two
    observations with different id_var values, all records with those id_var
    values are updated to the new consolidated value, even if they do not
    match by match_vars.

    If there is a missing value in any variable in match_vars, the
    observation is ignored in terms of the matching.


Example

    Suppose we have the following dataset,

          +-----------------------------------------------------------+
          | id          contact      phone    loc               email |
          |-----------------------------------------------------------|
          |  1   Picard, Michel   555-2222   home                     |
          |  1   Picard, Michel   555-3333   work                     |
          |  2   Picard, Robert   555-0001   home                     |
          |  2   Picard, Robert   555-1234   work                     |
          |  2   Picard, Robert                     picard@netbox.com |
          |  3    Pickard, John   555-5555   home                     |
          |  3    Pickard, John                      Pickard@here.com |
          |  4    Robert Picard   555-9999   cell                     |
          |  4    Robert Picard                     picard@netbox.com |
          +-----------------------------------------------------------+
  

    Each contact has a unique id but values 2 and 4 appear to refer to the
    same contact because the email is identical. Consolidating id values 2
    and 4 is a bit tricky because there are observations with those id values
    that are not part of the email match. However,

    . group_id id, matchby(email)

    . list, noobs sep(0)

          +-----------------------------------------------------------+
          | id          contact      phone    loc               email |
          |-----------------------------------------------------------|
          |  1   Picard, Michel   555-2222   home                     |
          |  1   Picard, Michel   555-3333   work                     |
          |  2   Picard, Robert   555-0001   home                     |
          |  2   Picard, Robert   555-1234   work                     |
          |  2   Picard, Robert                     picard@netbox.com |
          |  3    Pickard, John   555-5555   home                     |
          |  3    Pickard, John                      Pickard@here.com |
          |  2    Robert Picard   555-9999   cell                     |
          |  2    Robert Picard                     picard@netbox.com |
          +-----------------------------------------------------------+

    The listing shows that group_id has grouped the original id values 2 and
    4.  Other id values are unaffected.


Author

    Robert Picard
    picard@netbox.com