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10.1 Common Syntax

     Per input file:
     Once per command:
             /BY var_list[({D|A})] [var_list[({D|A}]]...

This section describes the syntactical features in common among the ADD FILES, MATCH FILES, and UPDATE commands. The following sections describe details specific to each command.

Each of these commands reads two or more input files and combines them. The command's output becomes the new active dataset. None of the commands actually change the input files. Therefore, if you want the changes to become permanent, you must explicitly save them using an appropriate procedure or transformation (see System and Portable File IO).

The syntax of each command begins with a specification of the files to be read as input. For each input file, specify FILE with a system file or portable file's name as a string, a dataset (see Datasets) or file handle name, (see File Handles), or an asterisk (‘*’) to use the active dataset as input. Use of portable files on FILE is a pspp extension.

At least two FILE subcommands must be specified. If the active dataset is used as an input source, then TEMPORARY must not be in effect.

Each FILE subcommand may be followed by any number of RENAME subcommands that specify a parenthesized group or groups of variable names as they appear in the input file, followed by those variables' new names, separated by an equals sign (=), e.g. /RENAME=(OLD1=NEW1)(OLD2=NEW2). To rename a single variable, the parentheses may be omitted: /RENAME=old=new. Within a parenthesized group, variables are renamed simultaneously, so that /RENAME=(A B=B A) exchanges the names of variables A and B. Otherwise, renaming occurs in left-to-right order.

Each FILE subcommand may optionally be followed by a single IN subcommand, which creates a numeric variable with the specified name and format F1.0. The IN variable takes value 1 in an output case if the given input file contributed to that output case, and 0 otherwise. The DROP, KEEP, and RENAME subcommands have no effect on IN variables.

If BY is used (see below), the SORT keyword must be specified after a FILE if that input file is not already sorted on the BY variables. When SORT is specified, pspp sorts the input file's data on the BY variables before it applies it to the command. When SORT is used, BY is required. SORT is a pspp extension.

pspp merges the dictionaries of all of the input files to form the dictionary of the new active dataset, like so:

The remaining subcommands apply to the output file as a whole, rather than to individual input files. They must be specified at the end of the command specification, following all of the FILE and related subcommands. The most important of these subcommands is BY, which specifies a set of one or more variables that may be used to find corresponding cases in each of the input files. The variables specified on BY must be present in all of the input files. Furthermore, if any of the input files are not sorted on the BY variables, then SORT must be specified for those input files.

The variables listed on BY may include (A) or (D) annotations to specify ascending or descending sort order. See SORT CASES, for more details on this notation. Adding (A) or (D) to the BY subcommand specification is a pspp extension.

The DROP subcommand can be used to specify a list of variables to exclude from the output. By contrast, the KEEP subcommand can be used to specify variables to include in the output; all variables not listed are dropped. DROP and KEEP are executed in left-to-right order and may be repeated any number of times. DROP and KEEP do not affect variables created by the IN, FIRST, and LAST subcommands, which are always included in the new active dataset, but they can be used to drop BY variables.

The FIRST and LAST subcommands are optional. They may only be specified on MATCH FILES and ADD FILES, and only when BY is used. FIRST and LIST each adds a numeric variable to the new active dataset, with the name given as the subcommand's argument and F1.0 print and write formats. The value of the FIRST variable is 1 in the first output case with a given set of values for the BY variables, and 0 in other cases. Similarly, the LAST variable is 1 in the last case with a given of BY values, and 0 in other cases.

When any of these commands creates an output case, variables that are only in files that are not present for the current case are set to the system-missing value for numeric variables or spaces for string variables.