= SPSS Looping =

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

<<TableOfContents>>

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== Arbitrary Lists ==

The [[SPSS/DoRepeat|DO REPEAT]] command can loop over arbitrary, fixed-length lists.

{{{
do repeat X='A' 'B' 'C' 'D' 'E'.
  if ltrim(rtrim(foo))=X bar=1.
end repeat.
}}}

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== Integer Ranges ==

The [[SPSS/DoRepeat|DO REPEAT]] command can loop over an integer range.

{{{
do repeat Y=1 to 5.
  if foo=X bar=1.
end repeat.
}}}

The [[SPSS/Loop|LOOP]] command can be used similarly.

{{{
loop #y=1 to 5 by 1.
  if foo=#y bar=1.
end loop.
}}}

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== Variable Lists ==

The [[SPSS/DoRepeat|DO REPEAT]] command can loop over variables. If the variables are not pre-existing, a range is extrapolated from the variable names.

{{{
do repeat Z=new1 to new5.
  compute Z=foo.
end repeat.
}}}

A similar effect can be acheived by using the [[SPSS/Loop|LOOP]] command with a [[SPSS/Vectors|vector]].

{{{
vector new(4).
loop #z = 1 to 4.
  compute new(#z) = (foo=#z).
end loop.
}}}

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== Conditional Looping ==

The [[SPSS/Loop|LOOP]] command can loop a variable number of times, based on either a 'while' or a 'break' condition. Specify the `IF` option on the `LOOP` command for the former behaviuor, or on the `END LOOP` command for the latter.

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

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

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== Indefinite Looping ==

The [[SPSS/Loop|LOOP]] command can also be made loop indefinitely, if no `IF` option is specified.

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

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== Macros ==

Advanced looping can be handled through macro programming. See [[SPSS/Macro/Looping|here]] for examples.



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