From: Ben Pfaff Date: Tue, 10 Jul 2007 13:17:59 +0000 (+0000) Subject: Improve N OF CASES documentation. X-Git-Tag: v0.6.0~394 X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3a8f4f7e938f1fc4a9d371cb1cdbe503c8cc60fe;p=pspp-builds.git Improve N OF CASES documentation. --- diff --git a/doc/data-selection.texi b/doc/data-selection.texi index e8430cf6..e7a12853 100644 --- a/doc/data-selection.texi +++ b/doc/data-selection.texi @@ -51,51 +51,31 @@ the next procedure or procedure-like 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. - -If the value specified for @cmd{N} is greater than the number of cases -read in, the value is ignored. - -@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. - -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.) - -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} 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. + +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. + +If the limit specified on @cmd{N OF CASES} is greater than the number +of cases in the active file, it has no effect. + +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. + +@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