@chapter Selecting data for analysis
This chapter documents PSPP commands that temporarily or permanently
-select data records from the active file for analysis.
+select data records from the active dataset for analysis.
@menu
* FILTER:: Exclude cases based on a variable.
-* N OF CASES:: Limit the size of the active file.
+* N OF CASES:: Limit the size of the active dataset.
* SAMPLE:: Select a specified proportion of cases.
* SELECT IF:: Permanently delete selected cases.
* SPLIT FILE:: Do multiple analyses with one command.
N [OF CASES] num_of_cases [ESTIMATED].
@end display
-Sometimes you may want to disregard cases of your input. @cmd{N} can
-do this. @code{N 100} tells PSPP to disregard all cases after the
-first 100.
+@cmd{N OF CASES} limits the number of cases processed by any
+procedures that follow it in the command stream. @code{N OF CASES
+100}, for example, tells PSPP to disregard all cases after the first
+100.
-If the value specified for @cmd{N} is greater than the number of cases
-read in, the value is ignored.
+When @cmd{N OF CASES} is specified after @cmd{TEMPORARY}, it affects
+only the next procedure (@pxref{TEMPORARY}). Otherwise, cases beyond
+the limit specified are not processed by any later procedure.
-@cmd{N} does not discard cases or prevent them from being read. It
-just causes cases beyond the last one specified to be ignored by data
-analysis commands.
+If the limit specified on @cmd{N OF CASES} is greater than the number
+of cases in the active dataset, it has no effect.
-A later @cmd{N} command can increase or decrease the number of cases
-selected. (To select all the cases without knowing how many there are,
-specify a very high number: 100000 or whatever you think is large enough.)
+When @cmd{N OF CASES} is used along with @cmd{SAMPLE} or @cmd{SELECT
+IF}, the case limit is applied to the cases obtained after sampling or
+case selection, regardless of how @cmd{N OF CASES} is placed relative
+to @cmd{SAMPLE} or @cmd{SELECT IF} in the command file. Thus, the
+commands @code{N OF CASES 100} and @code{SAMPLE .5} will both randomly
+sample approximately half of the active dataset's cases, then select the
+first 100 of those sampled, regardless of their order in the command
+file.
-Transformation procedures performed after @cmd{N} is executed
-@emph{do} cause cases to be discarded.
-
-@cmd{SAMPLE} and @cmd{SELECT IF} have
-precedence over @cmd{N}---the same results are obtained by both of the
-following fragments, given the same random number seeds:
-
-@example
-@i{@dots{}set up, read in data@dots{}}
-N 100.
-SAMPLE .5.
-@i{@dots{}analyze data@dots{}}
-
-@i{@dots{}set up, read in data@dots{}}
-SAMPLE .5.
-N 100.
-@i{@dots{}analyze data@dots{}}
-@end example
-
-Both fragments above first randomly sample approximately half of the
-cases, then select the first 100 of those sampled.
-
-@cmd{N} with the @code{ESTIMATED} keyword gives an
-estimated number of cases before @cmd{DATA LIST} or another command to
-read in data. @code{ESTIMATED} never limits the number of cases
-processed by procedures. PSPP currently does not make use of
-case count estimates.
-
-When @cmd{N} is specified after @cmd{TEMPORARY}, it affects only
-the next procedure (@pxref{TEMPORARY}).
+@cmd{N OF CASES} with the @code{ESTIMATED} keyword gives an estimated
+number of cases before @cmd{DATA LIST} or another command to read in
+data. @code{ESTIMATED} never limits the number of cases processed by
+procedures. PSPP currently does not make use of case count estimates.
@node SAMPLE
@section SAMPLE
@cmd{SAMPLE} randomly samples a proportion of the cases in the active
file. Unless it follows @cmd{TEMPORARY}, it operates as a
-transformation, permanently removing cases from the active file.
+transformation, permanently removing cases from the active dataset.
The proportion to sample can be expressed as a single number between 0
and 1. If @code{k} is the number specified, and @code{N} is the number
-of currently-selected cases in the active file, then after
+of currently-selected cases in the active dataset, then after
@code{SAMPLE @var{k}.}, approximately @code{k*N} cases will be
selected.
@enumerate
@item
If @var{N} is equal to the number of currently-selected cases in the
-active file, exactly @var{m} cases will be selected.
+active dataset, exactly @var{m} cases will be selected.
@item
If @var{N} is greater than the number of currently-selected cases in the
-active file, an equivalent proportion of cases will be selected.
+active dataset, an equivalent proportion of cases will be selected.
@item
If @var{N} is less than the number of currently-selected cases in the
active, exactly @var{m} cases will be selected @emph{from the first
-@var{N} cases in the active file.}
+@var{N} cases in the active dataset.}
@end enumerate
@cmd{SAMPLE} and @cmd{SELECT IF} are performed in
@cmd{SELECT IF} selects cases for analysis based on the value of a
boolean expression. Cases not selected are permanently eliminated
-from the active file, unless @cmd{TEMPORARY} is in effect
+from the active dataset, unless @cmd{TEMPORARY} is in effect
(@pxref{TEMPORARY}).
Specify a boolean expression (@pxref{Expressions}). If the value of the
you should first sort the data by that variable (@pxref{SORT CASES}).
Specify OFF to disable @cmd{SPLIT FILE} and resume analysis of the
-entire active file as a single group of data.
+entire active dataset as a single group of data.
When @cmd{SPLIT FILE} is specified after @cmd{TEMPORARY}, it affects only
the next procedure (@pxref{TEMPORARY}).
@cmd{TEMPORARY} is used to make the effects of transformations
following its execution temporary. These transformations will
affect only the execution of the next procedure or procedure-like
-command. Their effects will not be saved to the active file.
+command. Their effects will not be saved to the active dataset.
The only specification on @cmd{TEMPORARY} is the command name.
@end display
@cmd{WEIGHT} assigns cases varying weights,
-changing the frequency distribution of the active file. Execution of
+changing the frequency distribution of the active dataset. Execution of
@cmd{WEIGHT} is delayed until data have been read.
If a variable name is specified, @cmd{WEIGHT} causes the values of that
When @cmd{WEIGHT} is specified after @cmd{TEMPORARY}, it affects only
the next procedure (@pxref{TEMPORARY}).
-@cmd{WEIGHT} does not cause cases in the active file to be replicated in
-memory.
-@setfilename ignored
+@cmd{WEIGHT} does not cause cases in the active dataset to be
+replicated in memory.
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