Duplicate Cases (MATCH FILES command)

Duplicate cases are those with the same values for the key variables named on the BY subcommand.

• Duplicate cases are permitted in any input files except table files.
• When there is no table file, the first duplicate case in each file is matched with the first matching case (if any) from the other files; the second duplicate case is matched with a second matching duplicate, if any; and so on. (In effect, a parallel match is performed within groups of duplicate cases.) Unmatched cases are assigned system-missing values (for numeric variables) or blanks (for string variables) for variables from files that do not contain a match.
• The program displays a warning if it encounters duplicate keys in one or more of the files being matched.