-@node Data Selection, Conditionals and Looping, Data Manipulation, Top
+@node Data Selection
@chapter Selecting data for analysis
This chapter documents PSPP commands that temporarily or permanently
* WEIGHT:: Weight cases by a variable.
@end menu
-@node FILTER, N OF CASES, Data Selection, Data Selection
+@node FILTER
@section FILTER
@vindex FILTER
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 file, 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 file'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
differing endianness or floating-point formats. By default, the
random number seed is based on the system time.
-@node SELECT IF, SPLIT FILE, SAMPLE, Data Selection
+@node SELECT IF
@section SELECT IF
@vindex SELECT IF
(@pxref{TEMPORARY}), the @cmd{LAG} function may not be used
(@pxref{LAG}).
-@node SPLIT FILE, TEMPORARY, SELECT IF, Data Selection
+@node SPLIT FILE
@section SPLIT FILE
@vindex SPLIT FILE
When @cmd{SPLIT FILE} is specified after @cmd{TEMPORARY}, it affects only
the next procedure (@pxref{TEMPORARY}).
-@node TEMPORARY, WEIGHT, SPLIT FILE, Data Selection
+@node TEMPORARY
@section TEMPORARY
@vindex TEMPORARY
10.5, 13, 15. The data read by the first @cmd{DESCRIPTIVES} are 1, 2,
5, 7.5, 10, 12.
-@node WEIGHT, , TEMPORARY, Data Selection
+@node WEIGHT
@section WEIGHT
@vindex WEIGHT