@c PSPP - a program for statistical analysis.
-@c Copyright (C) 2017 Free Software Foundation, Inc.
+@c Copyright (C) 2017, 2020 Free Software Foundation, Inc.
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3
@c or any later version published by the Free Software Foundation;
The mode subcommand has two possible values: @subcmd{ADDVARIABLES} or @subcmd{REPLACE}.
In @subcmd{REPLACE} mode, the entire active dataset is replaced by a new dataset
which contains just the break variables and the destination varibles.
-In this mode, the new file will contain as many cases as there are
+In this mode, the new file contains as many cases as there are
unique combinations of the break variables.
-In @subcmd{ADDVARIABLES} mode, the destination variables will be appended to
+In @subcmd{ADDVARIABLES} mode, the destination variables are appended to
the existing active dataset.
Cases which have identical combinations of values in their break
-variables, will receive identical values for the destination variables.
-The number of cases in the active dataset will remain unchanged.
+variables, receive identical values for the destination variables.
+The number of cases in the active dataset remains unchanged.
Note that if @subcmd{ADDVARIABLES} is specified, then the data @emph{must} be
sorted on the break variables.
-By default, the active dataset will be sorted based on the break variables
+By default, the active dataset is sorted based on the break variables
before aggregation takes place. If the active dataset is already sorted
or otherwise grouped in terms of the break variables, specify
@subcmd{PRESORTED} to save time.
@subcmd{PRESORTED} is assumed if @subcmd{MODE=ADDVARIABLES} is used.
Specify @subcmd{DOCUMENT} to copy the documents from the active dataset into the
-aggregate file (@pxref{DOCUMENT}). Otherwise, the aggregate file will
+aggregate file (@pxref{DOCUMENT}). Otherwise, the aggregate file does
not contain any documents, even if the aggregate file replaces the
active dataset.
@item @subcmd{FIRST(@var{var_name})}
First non-missing value in break group. The aggregation variable
receives the complete dictionary information from the source variable.
-The sort performed by @cmd{AGGREGATE} (and by @cmd{SORT CASES}) is stable, so that
+The sort performed by @cmd{AGGREGATE} (and by @cmd{SORT CASES}) is stable.
+This means that
the first case with particular values for the break variables before
-sorting will also be the first case in that break group after sorting.
+sorting is also the first case in that break group after sorting.
@item @subcmd{FOUT(@var{var_name}, @var{low}, @var{high})}
Fraction of values strictly outside the specified range of constants.
@item @subcmd{LAST(@var{var_name})}
Last non-missing value in break group. The aggregation variable
receives the complete dictionary information from the source variable.
-The sort performed by @cmd{AGGREGATE} (and by @cmd{SORT CASES}) is stable, so that
-the last case with particular values for the break variables before
-sorting will also be the last case in that break group after sorting.
+The sort performed by @cmd{AGGREGATE} (and by @cmd{SORT CASES}) is stable.
@item @subcmd{MAX(@var{var_name})}
Maximum value. The aggregation variable receives the complete
The aggregation functions listed above exclude all user-missing values
from calculations. To include user-missing values, insert a period
-(@samp{.}) at the end of the function name. (e.g.@: @samp{SUM.}).
+(@samp{.}) at the end of the function name. (@i{e.g.}@: @samp{SUM.}).
(Be aware that specifying such a function as the last token on a line
-will cause the period to be interpreted as the end of the command.)
+causes the period to be interpreted as the end of the command.)
@cmd{AGGREGATE} both ignores and cancels the current @cmd{SPLIT FILE}
settings (@pxref{SPLIT FILE}).
+@subsection Aggregate Example
+
+The @file{personnel.sav} dataset provides the occupations and salaries of
+many individuals. For many purposes however such detailed information is
+not interesting, but often the aggregated statistics of each occupation are
+of interest. In @ref{aggregate:ex} the @cmd{AGGREGATE} command is used
+to calculate the mean, the median and the standard deviation of each
+occupation.
+
+@float Example, aggregate:ex
+@psppsyntax {aggregate.sps}
+@caption {Calculating aggregated statistics from the @file{personnel.sav} file.}
+@end float
+
+Since we chose the @samp{MODE = REPLACE} option, in @ref{aggregate:res} cases
+for the individual persons are no longer present. They have each been replaced
+by a single case per aggregated value.
+
+@float Results, aggregate:res
+@psppoutput {aggregate}
+@caption {Aggregated mean, median and standard deviation per @exvar{occupation}.}
+@end float
+
+Note that some values for the standard deviation are blank.
+This is because there is only one case with the respective
+occupation.
+
+
@node AUTORECODE
@section AUTORECODE
@vindex AUTORECODE
any user-missing values.
If @subcmd{/BLANK=MISSING} is given, then string variables which contain only
-whitespace are recoded as SYSMIS. If @subcmd{/BLANK=VALID} is given then they
-will be allocated a value like any other. @subcmd{/BLANK} is not relevant
+whitespace are recoded as SYSMIS. If @subcmd{/BLANK=VALID} is specified then they
+are allocated a value like any other. @subcmd{/BLANK} is not relevant
to numeric values. @subcmd{/BLANK=VALID} is the default.
@cmd{AUTORECODE} is a procedure. It causes the data to be read.
are generally a bad idea. One reason is that data entry errors are easily
overlooked. This has happened in @file{personnel.sav}; one entry which should
read ``Scientist'' has been mistyped as ``Scrientist''. In @ref{autorecode:ex}
-first, this error will be corrected,
+first, this error is corrected by the @cmd{DO IF} clause,
@footnote{One must use care when correcting such data input errors rather than
msimply marking them as missing. For example, if an occupation has been entered
``Barister'', did the person mean ``Barrister'' or did she mean ``Barista''?}
-then we will use @cmd{AUTORECODE} to
+then we use @cmd{AUTORECODE} to
create a new numeric variable which takes recoded values of @exvar{occupation}.
-Finally, we will remove the old variable and rename the new variable to
+Finally, we remove the old variable and rename the new variable to
the name of the old variable.
@float Example, autorecode:ex
For some purposes, neither height nor weight alone is of interest.
Epidemiologists are often more interested in the @dfn{body mass index} which
can sometimes be used as a predictor for clinical conditions.
-The body mass index is defined as the weight of the person in kg divided
+The body mass index is defined as the weight of the person in kilograms divided
by the square of the person's height in metres.
@footnote{Since BMI is a quantity with a ratio scale and has units, the term ``index''
is a misnomer, but that is what it is called.}
Mappings are considered from left to right.
Therefore, if a value is matched by a @var{src_value} from more than
-one mapping, the first (leftmost) mapping which matches will be considered.
-Any subsequent matches will be ignored.
+one mapping, the first (leftmost) mapping which matches is considered.
+Any subsequent matches are ignored.
The clause @samp{INTO @var{dest_vars}} is optional.
The behaviour of the command is slightly different depending on whether it
appears or not.
-If @samp{INTO @var{dest_vars}} does not appear, then values will be recoded
+If @samp{INTO @var{dest_vars}} does not appear, then values are recoded
``in place''.
This means that the recoded values are written back to the
source variables from whence the original values came.
of variables in @var{src_vars}
and the respective order of the variables in @var{dest_vars} corresponds to
the order of @var{src_vars}.
-That is to say, recoded values whose
-original value came from the @var{n}th variable in @var{src_vars} will be
+That is to say, the recoded value whose
+original value came from the @var{n}th variable in @var{src_vars} is
placed into the @var{n}th variable in @var{dest_vars}.
-The source variables will be unchanged.
+The source variables are unchanged.
If any mapping implies a string as its destination value, then the respective
destination variable must already exist, or
have been declared using @cmd{STRING} or another transformation.
-Numeric variables however will be automatically created if they don't already
+Numeric variables however are automatically created if they don't already
exist.
The following example deals with two source variables, @var{a} and @var{b}
which contain string values. Hence there are two destination variables
@var{v1} and @var{v2}.
Any cases where @var{a} or @var{b} contain the values @samp{apple},
-@samp{pear} or @samp{pomegranate} will result in @var{v1} or @var{v2} being
+@samp{pear} or @samp{pomegranate} result in @var{v1} or @var{v2} being
filled with the string @samp{fruit} whilst cases with
-@samp{tomato}, @samp{lettuce} or @samp{carrot} will result in @samp{vegetable}.
-Any other values will produce the result @samp{unknown}:
+@samp{tomato}, @samp{lettuce} or @samp{carrot} result in @samp{vegetable}.
+Any other values produce the result @samp{unknown}:
@example
string @var{v1} (a20).
string @var{v2} (a20).
must not refer to a string variable.
@samp{CONVERT} causes a number specified as a string to
be converted to a numeric value.
-For example it will convert the string @samp{"3"} into the numeric
-value 3 (note that it will not convert @samp{three} into 3).
+For example it converts the string @samp{"3"} into the numeric
+value 3 (note that it does not convert @samp{three} into 3).
If the string cannot be parsed as a number, then the system-missing value
is assigned instead.
In the following example, cases where the value of @var{x} (a string variable)
for ascending order. These apply to all the listed variables
up until the preceding @subcmd{(A)}, @subcmd{(D)}, @subcmd{(UP)} or @subcmd{(DOWN)}.
-The sort algorithms used by @cmd{SORT CASES} are stable. That is,
-records that have equal values of the sort variables will have the
-same relative order before and after sorting. As a special case,
-re-sorting an already sorted file will not affect the ordering of
+The sort algorithms used by @cmd{SORT CASES} are stable. This means
+records which have equal values of the sort variables have the
+same relative order before and after sorting. Thus,
+re-sorting an already sorted file does not affect the ordering of
cases.
@cmd{SORT CASES} is a procedure. It causes the data to be read.