1 @node Data Manipulation, Data Selection, Variable Attributes, Top
2 @chapter Data transformations
3 @cindex transformations
5 The PSPP procedures examined in this chapter manipulate data and
6 prepare the active file for later analyses. They do not produce output,
10 * AGGREGATE:: Summarize multiple cases into a single case.
11 * AUTORECODE:: Automatic recoding of variables.
12 * COMPUTE:: Assigning a variable a calculated value.
13 * COUNT:: Counting variables with particular values.
14 * FLIP:: Exchange variables with cases.
15 * IF:: Conditionally assigning a calculated value.
16 * RECODE:: Mapping values from one set to another.
17 * SORT CASES:: Sort the active file.
20 @node AGGREGATE, AUTORECODE, Data Manipulation, Data Manipulation
26 OUTFILE=@{*,'filename'@}
31 /dest_var['label']@dots{}=agr_func(src_vars, args@dots{})@dots{}
34 @cmd{AGGREGATE} summarizes groups of cases into single cases.
35 Cases are divided into groups that have the same values for one or more
36 variables called @dfn{break variables}. Several functions are available
37 for summarizing case contents.
39 The OUTFILE subcommand is required and must appear first. Specify a
40 system file by file name string or file handle (@pxref{FILE HANDLE}).
41 The aggregated cases are written to this file. If @samp{*} is
42 specified, then the aggregated cases replace the active file.
44 By default, the active file will be sorted based on the break variables
45 before aggregation takes place. If the active file is already sorted
46 or otherwise grouped in terms of the break variables, specify
47 PRESORTED to save time.
49 Specify DOCUMENT to copy the documents from the active file into the
50 aggregate file (@pxref{DOCUMENT}). Otherwise, the aggregate file will
51 not contain any documents, even if the aggregate file replaces the
54 Normally, only a single case (for SD and SD., two cases) need be
55 non-missing in each group for the aggregate variable to be
56 non-missing. Specifying /MISSING=COLUMNWISE inverts this behavior, so
57 that the aggregate variable becomes missing if any aggregated value is
60 If PRESORTED, DOCUMENT, or MISSING are specified, they must appear
61 between OUTFILE and BREAK.
63 At least one break variable must be specified on BREAK, a
64 required subcommand. The values of these variables are used to divide
65 the active file into groups to be summarized. In addition, at least
66 one @var{dest_var} must be specified.
68 One or more sets of aggregation variables must be specified. Each set
69 comprises a list of aggregation variables, an equals sign (@samp{=}),
70 the name of an aggregation function (see the list below), and a list
71 of source variables in parentheses. Some aggregation functions expect
72 additional arguments following the source variable names.
74 Aggregation variables typically are created with no variable label,
75 value labels, or missing values. Their default print and write
76 formats depend on the aggregation function used, with details given in
77 the table below. A variable label for an aggregation variable may be
78 specified just after the variable's name in the aggregation variable
81 Each set must have exactly as many source variables as aggregation
82 variables. Each aggregation variable receives the results of applying
83 the specified aggregation function to the corresponding source
84 variable. The MEAN, SD, and SUM aggregation functions may only be
85 applied to numeric variables. All the rest may be applied to numeric
86 and short and long string variables.
88 The available aggregation functions are as follows:
91 @item FGT(var_name, value)
92 Fraction of values greater than the specified constant. The default
95 @item FIN(var_name, low, high)
96 Fraction of values within the specified inclusive range of constants.
97 The default format is F5.3.
99 @item FLT(var_name, value)
100 Fraction of values less than the specified constant. The default
103 @item FIRST(var_name)
104 First non-missing value in break group. The aggregation variable
105 receives the complete dictionary information from the source variable.
107 @item FOUT(var_name, low, high)
108 Fraction of values strictly outside the specified range of constants.
109 The default format is F5.3.
112 Last non-missing value in break group. The aggregation variable
113 receives the complete dictionary information from the source variable.
116 Maximum value. The aggregation variable receives the complete
117 dictionary information from the source variable.
120 Arithmetic mean. Limited to numeric values. The default format is
124 Minimum value. The aggregation variable receives the complete
125 dictionary information from the source variable.
128 Number of non-missing values. The default format is F7.0 if weighting
129 is not enabled, F8.2 if it is (@pxref{WEIGHT}).
132 Number of cases aggregated to form this group. The default format is
133 F7.0 if weighting is not enabled, F8.2 if it is (@pxref{WEIGHT}).
135 @item NMISS(var_name)
136 Number of missing values. The default format is F7.0 if weighting is
137 not enabled, F8.2 if it is (@pxref{WEIGHT}).
140 Number of non-missing values. Each case is considered to have a weight
141 of 1, regardless of the current weighting variable (@pxref{WEIGHT}).
142 The default format is F7.0.
145 Number of cases aggregated to form this group. Each case is considered
146 to have a weight of 1, regardless of the current weighting variable.
147 The default format is F7.0.
149 @item NUMISS(var_name)
150 Number of missing values. Each case is considered to have a weight of
151 1, regardless of the current weighting variable. The default format is F7.0.
153 @item PGT(var_name, value)
154 Percentage between 0 and 100 of values greater than the specified
155 constant. The default format is F5.1.
157 @item PIN(var_name, low, high)
158 Percentage of values within the specified inclusive range of
159 constants. The default format is F5.1.
161 @item PLT(var_name, value)
162 Percentage of values less than the specified constant. The default
165 @item POUT(var_name, low, high)
166 Percentage of values strictly outside the specified range of
167 constants. The default format is F5.1.
170 Standard deviation of the mean. Limited to numeric values. The
171 default format is F8.2.
174 Sum. Limited to numeric values. The default format is F8.2.
177 Aggregation functions compare string values in terms of internal
178 character codes. On most modern computers, this is a form of ASCII.
180 The aggregation functions listed above exclude all user-missing values
181 from calculations. To include user-missing values, insert a period
182 (@samp{.}) at the end of the function name. (e.g.@: @samp{SUM.}).
183 (Be aware that specifying such a function as the last token on a line
184 will cause the period to be interpreted as the end of the command.)
186 @cmd{AGGREGATE} both ignores and cancels the current @cmd{SPLIT FILE}
187 settings (@pxref{SPLIT FILE}).
189 @node AUTORECODE, COMPUTE, AGGREGATE, Data Manipulation
194 AUTORECODE VARIABLES=src_vars INTO dest_vars
199 The @cmd{AUTORECODE} procedure considers the @var{n} values that a variable
200 takes on and maps them onto values 1@dots{}@var{n} on a new numeric
203 Subcommand VARIABLES is the only required subcommand and must come
204 first. Specify VARIABLES, an equals sign (@samp{=}), a list of source
205 variables, INTO, and a list of target variables. There must the same
206 number of source and target variables. The target variables must not
209 By default, increasing values of a source variable (for a string, this
210 is based on character code comparisons) are recoded to increasing values
211 of its target variable. To cause increasing values of a source variable
212 to be recoded to decreasing values of its target variable (@var{n} down
213 to 1), specify DESCENDING.
215 PRINT is currently ignored.
217 @cmd{AUTORECODE} is a procedure. It causes the data to be read.
219 @node COMPUTE, COUNT, AUTORECODE, Data Manipulation
224 COMPUTE variable = expression.
226 COMPUTE vector(index) = expression.
229 @cmd{COMPUTE} assigns the value of an expression to a target
230 variable. For each case, the expression is evaluated and its value
231 assigned to the target variable. Numeric and short and long string
232 variables may be assigned. When a string expression's width differs
233 from the target variable's width, the string result of the expression
234 is truncated or padded with spaces on the right as necessary. The
235 expression and variable types must match.
237 For numeric variables only, the target variable need not already
238 exist. Numeric variables created by @cmd{COMPUTE} are assigned an
239 @code{F8.2} output format. String variables must be declared before
240 they can be used as targets for @cmd{COMPUTE}.
242 The target variable may be specified as an element of a vector
243 (@pxref{VECTOR}). In this case, a vector index expression must be
244 specified in parentheses following the vector name. The index
245 expression must evaluate to a numeric value that, after rounding down
246 to the nearest integer, is a valid index for the named vector.
248 Using @cmd{COMPUTE} to assign to a variable specified on @cmd{LEAVE}
249 (@pxref{LEAVE}) resets the variable's left state. Therefore,
250 @code{LEAVE} should be specified following @cmd{COMPUTE}, not before.
252 @cmd{COMPUTE} is a transformation. It does not cause the active file to be
255 When @cmd{COMPUTE} is specified following @cmd{TEMPORARY}
256 (@pxref{TEMPORARY}), the @cmd{LAG} function may not be used
259 @node COUNT, FLIP, COMPUTE, Data Manipulation
264 COUNT var_name = var@dots{} (value@dots{}).
266 Each value takes one of the following forms:
272 In addition, num1 and num2 can be LO or LOWEST, or HI or HIGHEST,
276 @cmd{COUNT} creates or replaces a numeric @dfn{target} variable that
277 counts the occurrence of a @dfn{criterion} value or set of values over
278 one or more @dfn{test} variables for each case.
280 The target variable values are always nonnegative integers. They are
281 never missing. The target variable is assigned an F8.2 output format.
282 @xref{Input/Output Formats}. Any variables, including long and short
283 string variables, may be test variables.
285 User-missing values of test variables are treated just like any other
286 values. They are @strong{not} treated as system-missing values.
287 User-missing values that are criterion values or inside ranges of
288 criterion values are counted as any other values. However (for numeric
289 variables), keyword MISSING may be used to refer to all system-
290 and user-missing values.
292 @cmd{COUNT} target variables are assigned values in the order
293 specified. In the command @code{COUNT A=A B(1) /B=A B(2).}, the
294 following actions occur:
298 The number of occurrences of 1 between @code{A} and @code{B} is counted.
301 @code{A} is assigned this value.
304 The number of occurrences of 1 between @code{B} and the @strong{new}
305 value of @code{A} is counted.
308 @code{B} is assigned this value.
311 Despite this ordering, all @cmd{COUNT} criterion variables must exist
312 before the procedure is executed---they may not be created as target
313 variables earlier in the command! Break such a command into two
316 The examples below may help to clarify.
320 Assuming @code{Q0}, @code{Q2}, @dots{}, @code{Q9} are numeric variables,
321 the following commands:
325 Count the number of times the value 1 occurs through these variables
326 for each case and assigns the count to variable @code{QCOUNT}.
329 Print out the total number of times the value 1 occurs throughout
330 @emph{all} cases using @cmd{DESCRIPTIVES}. @xref{DESCRIPTIVES}, for
335 COUNT QCOUNT=Q0 TO Q9(1).
336 DESCRIPTIVES QCOUNT /STATISTICS=SUM.
340 Given these same variables, the following commands:
344 Count the number of valid values of these variables for each case and
345 assigns the count to variable @code{QVALID}.
348 Multiplies each value of @code{QVALID} by 10 to obtain a percentage of
349 valid values, using @cmd{COMPUTE}. @xref{COMPUTE}, for details.
352 Print out the percentage of valid values across all cases, using
353 @cmd{DESCRIPTIVES}. @xref{DESCRIPTIVES}, for details.
357 COUNT QVALID=Q0 TO Q9 (LO THRU HI).
358 COMPUTE QVALID=QVALID*10.
359 DESCRIPTIVES QVALID /STATISTICS=MEAN.
363 @node FLIP, IF, COUNT, Data Manipulation
368 FLIP /VARIABLES=var_list /NEWNAMES=var_name.
371 @cmd{FLIP} transposes rows and columns in the active file. It
372 causes cases to be swapped with variables, and vice versa.
374 All variables in the transposed active file are numeric. String
375 variables take on the system-missing value in the transposed file.
377 No subcommands are required. If specified, the VARIABLES subcommand
378 selects variables to be transformed into cases, and variables not
379 specified are discarded. If the VARIABLES subcommand is omitted, all
380 variables are selected for transposition.
382 The variables specified by NEWNAMES, which must be a string variable, is
383 used to give names to the variables created by @cmd{FLIP}. If
385 specified then the default is a variable named CASE_LBL, if it exists.
386 If it does not then the variables created by FLIP are named VAR000
387 through VAR999, then VAR1000, VAR1001, and so on.
389 When a NEWNAMES variable is available, the names must be canonicalized
390 before becoming variable names. Invalid characters are replaced by
391 letter @samp{V} in the first position, or by @samp{_} in subsequent
392 positions. If the name thus generated is not unique, then numeric
393 extensions are added, starting with 1, until a unique name is found or
394 there are no remaining possibilities. If the latter occurs then the
395 FLIP operation aborts.
397 The resultant dictionary contains a CASE_LBL variable, which stores the
398 names of the variables in the dictionary before the transposition. If
399 the active file is subsequently transposed using @cmd{FLIP}, this
401 be used to recreate the original variable names.
403 FLIP honors @cmd{N OF CASES} (@pxref{N OF CASES}). It ignores
404 @cmd{TEMPORARY} (@pxref{TEMPORARY}), so that ``temporary''
405 transformations become permanent.
407 @node IF, RECODE, FLIP, Data Manipulation
412 IF condition variable=expression.
414 IF condition vector(index)=expression.
417 The @cmd{IF} transformation conditionally assigns the value of a target
418 expression to a target variable, based on the truth of a test
421 Specify a boolean-valued expression (@pxref{Expressions}) to be tested
422 following the IF keyword. This expression is evaluated for each case.
423 If the value is true, then the value of the expression is computed and
424 assigned to the specified variable. If the value is false or missing,
425 nothing is done. Numeric and short and long string variables may be
426 assigned. When a string expression's width differs from the target
427 variable's width, the string result of the expression is truncated or
428 padded with spaces on the right as necessary. The expression and
429 variable types must match.
431 The target variable may be specified as an element of a vector
432 (@pxref{VECTOR}). In this case, a vector index expression must be
433 specified in parentheses following the vector name. The index
434 expression must evaluate to a numeric value that, after rounding down
435 to the nearest integer, is a valid index for the named vector.
437 Using @cmd{IF} to assign to a variable specified on @cmd{LEAVE}
438 (@pxref{LEAVE}) resets the variable's left state. Therefore,
439 @code{LEAVE} should be specified following @cmd{IF}, not before.
441 When @cmd{IF} is specified following @cmd{TEMPORARY}
442 (@pxref{TEMPORARY}), the @cmd{LAG} function may not be used
445 @node RECODE, SORT CASES, IF, Data Manipulation
450 RECODE var_list (src_value@dots{}=dest_value)@dots{} [INTO var_list].
452 src_value may take the following forms:
459 Open-ended ranges may be specified using LO or LOWEST for num1
460 or HI or HIGHEST for num2.
462 dest_value may take the following forms:
469 @cmd{RECODE} translates data from one range of values to
470 another, via flexible user-specified mappings. Data may be remapped
471 in-place or copied to new variables. Numeric, short string, and long
472 string data can be recoded.
474 Specify the list of source variables, followed by one or more mapping
475 specifications each enclosed in parentheses. If the data is to be
476 copied to new variables, specify INTO, then the list of target
477 variables. String target variables must already have been declared
478 using @cmd{STRING} or another transformation, but numeric target
480 be created on the fly. There must be exactly as many target variables
481 as source variables. Each source variable is remapped into its
482 corresponding target variable.
484 When INTO is not used, the input and output variables must be of the
485 same type. Otherwise, string values can be recoded into numeric values,
486 and vice versa. When this is done and there is no mapping for a
487 particular value, either a value consisting of all spaces or the
488 system-missing value is assigned, depending on variable type.
490 Mappings are considered from left to right. The first src_value that
491 matches the value of the source variable causes the target variable to
492 receive the value indicated by the dest_value. Literal number, string,
493 and range src_value's should be self-explanatory. MISSING as a
494 src_value matches any user- or system-missing value. SYSMIS matches the
495 system missing value only. ELSE is a catch-all that matches anything.
496 It should be the last src_value specified.
498 Numeric and string dest_value's should also be self-explanatory. COPY
499 causes the input values to be copied to the output. This is only value
500 if the source and target variables are of the same type. SYSMIS
501 indicates the system-missing value.
503 If the source variables are strings and the target variables are
504 numeric, then there is one additional mapping available: (CONVERT),
505 which must be the last specified mapping. CONVERT causes a number
506 specified as a string to be converted to a numeric value. If the string
507 cannot be parsed as a number, then the system-missing value is assigned.
509 Multiple recodings can be specified on a single @cmd{RECODE} invocation.
510 Introduce additional recodings with a slash (@samp{/}) to
511 separate them from the previous recodings.
513 @node SORT CASES, , RECODE, Data Manipulation
518 SORT CASES BY var_list.
521 @cmd{SORT CASES} sorts the active file by the values of one or more
524 Specify BY and a list of variables to sort by. By default, variables
525 are sorted in ascending order. To override sort order, specify (D) or
526 (DOWN) after a list of variables to get descending order, or (A) or (UP)
527 for ascending order. These apply to the entire list of variables
530 The sort algorithms used by @cmd{SORT CASES} are stable. That is,
531 records that have equal values of the sort variables will have the
532 same relative order before and after sorting. As a special case,
533 re-sorting an already sorted file will not affect the ordering of
536 @cmd{SORT CASES} is a procedure. It causes the data to be read.
538 @cmd{SORT CASES} attempts to sort the entire active file in main memory.
539 If workspace is exhausted, it falls back to a merge sort algorithm that
540 involves creates numerous temporary files.
542 @cmd{SORT CASES} may not be specified following TEMPORARY.