Dynamically create variable names in loops - SPSS
I have many variables with names like
PRE_adam
POST_adam
PRE_betty
POST_betty
PRE_clara
POST_clara
...
for many people names.
I want to calculate the difference between PRE_X
and POST_X
for a list X
- something like this:
COMPUTE DIFF_adam = POST_adam - PRE_adam
COMPUTE DIFF_betty = POST_betty - PRE_betty
COMPUTE DIFF_clara = POST_clara - PRE_clara
Is there a way to do this in a loop? Something like that:
DO REPEAT x= adam betty clara
COMPUTE !concat('DIFF_',x) = !concat('POST_',x) - !concat('PRE_',x)
END REPEAT
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You are mistakenly trying to use the SPSS language macro ( DEFINE /! ENDDEFINE ) in normal SPSS syntax, i.e.! concat only works when used in the body of an SPSS macro.
Here is a non-python solution using DEFINE /! ENDDEFINE: But this requires entering names.
/*** ############################## ***/.
DATA LIST FREE/ PRE_adam
POST_adam
PRE_betty
POST_betty
PRE_clara
POST_clara.
BEGIN DATA
1 3 15 27 19 31
2 4 16 18 20 42
END DATA.
/*** ############################## ***/.
/*** ############################## ***/.
define !CompDiff (names=!cmdend)
!do !i !in (!names)
compute !concat("DIFF_",!i)=!concat('POST_',!i) - !concat('PRE_',!i).
!doend
exe.
!enddefine.
/*** ############################## ***/.
set mprint on.
!CompDiff names=adam betty clara.
Here's a more "dynamic" solution that reads the PRE and POST values in the active dataset and automatically calculates the difference, but depends on the python installation:
begin program.
import spss, spssaux, spssdata
spss.Submit("set mprint on.")
preVars=spssaux.VariableDict(pattern="PRE",caseless=True).variables
postVars=spssaux.VariableDict(pattern="POST",caseless=True).variables
if len(preVars) != len(preVars):
raise ValueError("Mis-match number of PRE and POST vars")
for preVar, postVar in zip(sorted(preVars),sorted(postVars)):
preName=preVar[preVar.index("_")+1:]
postName=postVar[postVar.index("_")+1:]
if preName != postName:
raise ValueError("Mis-match NAMES of PRE and POST vars")
spss.Submit("compute DIFF_%(preName)s=POST_%(preName)s - PRE_%(preName)s." % locals())
spss.Submit("set mprint off.")
end program.
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