Differences between revisions 1 and 7 (spanning 6 versions)

SPSS Looping

SPSS offers a couple options for looping, but overall is less flexible as compared to other languages.

Contents

SPSS Looping

Do Repeat

The DO REPEAT ... END REPEAT command loops over...

arbitrary sequences
variable ranges (either existing or new)
integer ranges

This command is only valid for data transformation commands (i.e. COMPUTE).

Multiple sequences/ranges can be iterated over in parallel as long as each has the same number of elements.

do repeat X=A B C D E / Y=new1 to new5 / Z=1 to 5.
  if (original=Z) Y=ltrim(rtrim(X)).
end repeat.

To print the evaluated loop syntax, use END REPEAT PRINT.

Because only transformation commands are valid inside DO REPEAT, it isn't possible to do nested looping with it.

Loop

The LOOP ... END LOOP command can arbitrarily loop.

Indefinite Looping

The LOOP command on its own will loop indefinitely (but actually until a maximum depth is reached). A warning will be emitted.

loop.
  compute sentence = replace(sentence,'  ',' ').
end loop.

While Loop

There are two options for a conditional while loop.

First, use the if subcommand on END LOOP. Note that this will still run once, as the condition won't be checked until then.

loop.
  compute sentence = replace(sentence,'  ',' ').
end loop if char.index(sentence,'  ') = 0.

Second, use the if subcommand on LOOP.

loop if char.index(sentence,'  ') > 0.
  compute sentence = replace(sentence,'  ',' ').
end loop.

Integer Range

An explicit number of repetitions can be specified.

loop X=1 to 3.
  compute sentence = replace(sentence,'  ',' ').
end loop.

The variable X is created by the LOOP command and it will persist in the dataset. In the above example it will have a final value of 4. To avoid persistence, consider using a scratch variable (i.e. #i).

The full specification is LOOP <VARIABLE> = <START> TO <END> BY <STEP>.

Variable Range

The integer range method can be combined with vectors to achieve looping over variables.

vector new(4).
loop #i = 1 to 4.
  compute new(#i) = (original=#i).
end loop.

Macros

Advanced looping can be handled through macro programming. See here for examples.

CategoryRicottone

-  ⇤ ← Revision 1 as of 2021-10-01 15:05:46 → 
  Size: 918
  Editor: DominicRicottone
  Comment:
+   ← Revision 7 as of 2023-06-10 13:26:54 → ⇥
  Size: 2536
  Editor: DominicRicottone
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
 Line 3:
-SPSS offers a couple options for looping, but overall is less flexible as compared to other languages.
+SPSS offers a couple options for '''looping''', but overall is less flexible as compared to other languages.
 Line 11:
-== DO REPEAT ==
+== Do Repeat ==
 Line 13:
-One method of printing that is '''only valid for data transformation commands''' (i.e. `COMPUTE`) is the `DO REPEAT ... END REPEAT` command.
+The '''`DO REPEAT ... END REPEAT`''' command loops over...
 Line 15:
-As demonstrated below, `DO REPEAT` can iterate over...
-Line 19:
+Line 18:
+This command is ''only valid for data transformation commands'' (i.e. `COMPUTE`).
-Line 30:
+Line 31:
+Because only transformation commands are valid inside `DO REPEAT`, it isn't possible to do nested looping with it.

----



== Loop ==

The '''`LOOP ... END LOOP`''' command can arbitrarily loop.



=== Indefinite Looping ===

The `LOOP` command on its own will loop indefinitely (but actually until a maximum depth is reached). A warning will be emitted.

{{{
loop.
  compute sentence = replace(sentence,'  ',' ').
end loop.
}}}



===  While Loop ===

There are two options for a conditional while loop.

First, use the `if` subcommand on `END LOOP`. Note that this will still run once, as the condition won't be checked until then.

{{{
loop.
  compute sentence = replace(sentence,'  ',' ').
end loop if char.index(sentence,'  ') = 0.
}}}

Second, use the `if` subcommand on `LOOP`.

{{{
loop if char.index(sentence,'  ') > 0.
  compute sentence = replace(sentence,'  ',' ').
end loop.
}}}



=== Integer Range ===

An explicit number of repetitions can be specified.

{{{
loop X=1 to 3.
  compute sentence = replace(sentence,'  ',' ').
end loop.
}}}

The variable `X` is created by the `LOOP` command and it will persist in the dataset. In the above example it will have a final value of 4. To avoid persistence, consider using a [[SPSS/ScratchVariables|scratch variable]] (i.e. `#i`).

The full specification is `LOOP <VARIABLE> = <START> TO <END> BY <STEP>`.



=== Variable Range ===

The integer range method can be combined with [[SPSS/Vectors|vectors]] to achieve looping over variables.

{{{
vector new(4).
loop #i = 1 to 4.
  compute new(#i) = (original=#i).
end loop.
}}}
-Line 36:
+Line 110:
-Advanced looping can be handled through macro programming. See [[SPSS/Macros#Loops]] for examples.
+Advanced looping can be handled through macro programming. See [[SPSS/Macro/Looping|here]] for examples.

Diff for "SPSS/Looping"