Setting bits in SPSS variable

[Mike Pritchard]

Is there an easy way to set bits in a an SPSS variable?  I’m trying to create a variable based on the combinations of other (dichotomous) variables.  The way that seems logically easy to me is to set a bit for each of the variables, and then the output variable will automatically represent the correct combination.  Thus (pseudo code)

 

IF (VarA) COMPUTE Comb = Comb AND 1.

IF (VarB) COMPUTE Comb = Comb AND 2.

IF (VarC) COMPUTE Comb = Comb AND 4.

 

Etc.

 

But I can’t figure out how to do this.  Instead, I’m using all the combinations with individual IF statements which works for a small number, but isn’t very scalable and is easy to make mistakes.

 

COMPUTE Comb=$SYSMIS.

IF ((VarA=1) AND (VarB=1) AND (VarC=1)) Comb=7.

IF ((VarA=1) AND (VarB=1) AND (VarC=0)) Comb=6.

IF ((VarA=1) AND (VarB=0) AND (VarC=1)) Comb=5.

IF ((VarA=1) AND (VarB=0) AND (VarC=0)) Comb=4.

IF ((VarA=0) AND (VarB=1) AND (VarC=1)) Comb=3.

IF ((VarA=0) AND (VarB=1) AND (VarC=0)) Comb=2.

IF ((VarA=0) AND (VarB=0) AND (VarC=1)) Comb=1.

IF ((VarA=0) AND (VarB=0) AND (VarC=0)) Comb=0.

EXECUTE .

 

As usual with my questions, this feels like something that should be obvious.

 

Thanks in advance.

Mike

 

_________________________________________________________________________
Mike Pritchard | [hidden email] | 5 Circles Research | 425-444-3410 (c) | 425-968-3883 (o)
Research to help companies build products that people buy

[Jon K Peck]

It all depends on what you are really going to do with this packed form, but typically one would combine these as powers of 2.  E.g.,
compute comb = a * 2**0 + b * 2**1 + c * 2**2 + ....

SPSS does not provide direct operations on bits as suggested in your pseudocode, but I think you meant OR there rather than AND.

If you really want to do bit packing, you could use the packDummies and extractDummies function in the extendedTransforms.py module available from the SPSS Community website in the Python modules collection.  These could conveniently be used in a transformation with the SPSSINC TRANS extension command.

HTH,


Jon Peck (no "h") aka Kim
Senior Software Engineer, IBM
[hidden email]
new phone: [phone]




From:        Mike Pritchard <[hidden email]>
To:        [hidden email]
Date:        04/01/2012 12:37 PM
Subject:        [SPSSX-L] Setting bits in SPSS variable
Sent by:        "SPSSX(r) Discussion" <[hidden email]>

---

Is there an easy way to set bits in a an SPSS variable?  I’m trying to create a variable based on the combinations of other (dichotomous) variables.  The way that seems logically easy to me is to set a bit for each of the variables, and then the output variable will automatically represent the correct combination.  Thus (pseudo code)
 
IF (VarA) COMPUTE Comb = Comb AND 1.
IF (VarB) COMPUTE Comb = Comb AND 2.
IF (VarC) COMPUTE Comb = Comb AND 4.
 
Etc.
 
But I can’t figure out how to do this.  Instead, I’m using all the combinations with individual IF statements which works for a small number, but isn’t very scalable and is easy to make mistakes.
 
COMPUTE Comb=$SYSMIS.
IF ((VarA=1) AND (VarB=1) AND (VarC=1)) Comb=7.
IF ((VarA=1) AND (VarB=1) AND (VarC=0)) Comb=6.
IF ((VarA=1) AND (VarB=0) AND (VarC=1)) Comb=5.
IF ((VarA=1) AND (VarB=0) AND (VarC=0)) Comb=4.
IF ((VarA=0) AND (VarB=1) AND (VarC=1)) Comb=3.
IF ((VarA=0) AND (VarB=1) AND (VarC=0)) Comb=2.
IF ((VarA=0) AND (VarB=0) AND (VarC=1)) Comb=1.
IF ((VarA=0) AND (VarB=0) AND (VarC=0)) Comb=0.
EXECUTE .
 
As usual with my questions, this feels like something that should be obvious.
 
Thanks in advance.
Mike
 
_________________________________________________________________________
Mike Pritchard | mikep@... | 5 Circles Research | 425-444-3410 (c) | 425-968-3883 (o)
Research to help companies build products that people buy

[Maguin, Eugene]

Mike,

There a couple of different ways of doing something like what you want. Assuming VarA-VarC has value 0,1.

Using strings.

String comb(a3).

Compute comb=concat(string(vara,f1.0), string(varb,f1.0), string(varc,f1.0)).

 

Using numeric

Compute comb=100*vara+10*varb+varc.

 

Gene Maguin

 

From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Mike Pritchard
Sent: Sunday, April 01, 2012 2:34 PM
To: [hidden email]
Subject: Setting bits in SPSS variable

 

Is there an easy way to set bits in a an SPSS variable?  I’m trying to create a variable based on the combinations of other (dichotomous) variables.  The way that seems logically easy to me is to set a bit for each of the variables, and then the output variable will automatically represent the correct combination.  Thus (pseudo code)

 

IF (VarA) COMPUTE Comb = Comb AND 1.

IF (VarB) COMPUTE Comb = Comb AND 2.

IF (VarC) COMPUTE Comb = Comb AND 4.

 

Etc.

 

But I can’t figure out how to do this.  Instead, I’m using all the combinations with individual IF statements which works for a small number, but isn’t very scalable and is easy to make mistakes.

 

COMPUTE Comb=$SYSMIS.

IF ((VarA=1) AND (VarB=1) AND (VarC=1)) Comb=7.

IF ((VarA=1) AND (VarB=1) AND (VarC=0)) Comb=6.

IF ((VarA=1) AND (VarB=0) AND (VarC=1)) Comb=5.

IF ((VarA=1) AND (VarB=0) AND (VarC=0)) Comb=4.

IF ((VarA=0) AND (VarB=1) AND (VarC=1)) Comb=3.

IF ((VarA=0) AND (VarB=1) AND (VarC=0)) Comb=2.

IF ((VarA=0) AND (VarB=0) AND (VarC=1)) Comb=1.

IF ((VarA=0) AND (VarB=0) AND (VarC=0)) Comb=0.

EXECUTE .

 

As usual with my questions, this feels like something that should be obvious.

 

Thanks in advance.

Mike

 

_________________________________________________________________________
Mike Pritchard | [hidden email] | 5 Circles Research | 425-444-3410 (c) | 425-968-3883 (o)
Research to help companies build products that people buy

[Mike Pritchard]

Jon, Gene,

Thanks for the suggestions. I think I must have had a brain spasm, because I forgot that each response would only be evaluated once – hence your approaches were what I should have come up with.

 

Jon, I probably used poor pseudo code for setting the bits – based on the operators in SPSS – but you are correct from other languages.

 

I just created a new variable using the simpler syntax to confirm that the same results are generated.

 

Thanks!

Mike

 

 

_________________________________________________________________________
Mike Pritchard | [hidden email] | 5 Circles Research | 425-444-3410 (c) | 425-968-3883 (o)
Research to help companies build products that people buy

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From: Jon K Peck [mailto:[hidden email]]
Sent: Sunday, April 01, 2012 11:56 AM
To: Mike Pritchard
Cc: [hidden email]
Subject: Re: [SPSSX-L] Setting bits in SPSS variable

 

It all depends on what you are really going to do with this packed form, but typically one would combine these as powers of 2.  E.g.,
compute comb = a * 2**0 + b * 2**1 + c * 2**2 + ....

SPSS does not provide direct operations on bits as suggested in your pseudocode, but I think you meant OR there rather than AND.

If you really want to do bit packing, you could use the packDummies and extractDummies function in the extendedTransforms.py module available from the SPSS Community website in the Python modules collection.  These could conveniently be used in a transformation with the SPSSINC TRANS extension command.

HTH,


Jon Peck (no "h") aka Kim
Senior Software Engineer, IBM
[hidden email]
new phone: [phone]

Mike,

There a couple of different ways of doing something like what you want. Assuming VarA-VarC has value 0,1.

Using strings.

String comb(a3).

Compute comb=concat(string(vara,f1.0), string(varb,f1.0), string(varc,f1.0)).

 

Using numeric

Compute comb=100*vara+10*varb+varc.

 

Gene Maguin

 

From:        Mike Pritchard <[hidden email]>
To:        [hidden email]
Date:        04/01/2012 12:37 PM
Subject:        [SPSSX-L] Setting bits in SPSS variable
Sent by:        "SPSSX(r) Discussion" <[hidden email]>

---

Is there an easy way to set bits in a an SPSS variable?  I’m trying to create a variable based on the combinations of other (dichotomous) variables.  The way that seems logically easy to me is to set a bit for each of the variables, and then the output variable will automatically represent the correct combination.  Thus (pseudo code)
 
IF (VarA) COMPUTE Comb = Comb AND 1.
IF (VarB) COMPUTE Comb = Comb AND 2.
IF (VarC) COMPUTE Comb = Comb AND 4.
 
Etc.
 
But I can’t figure out how to do this.  Instead, I’m using all the combinations with individual IF statements which works for a small number, but isn’t very scalable and is easy to make mistakes.
 
COMPUTE Comb=$SYSMIS.
IF ((VarA=1) AND (VarB=1) AND (VarC=1)) Comb=7.
IF ((VarA=1) AND (VarB=1) AND (VarC=0)) Comb=6.
IF ((VarA=1) AND (VarB=0) AND (VarC=1)) Comb=5.
IF ((VarA=1) AND (VarB=0) AND (VarC=0)) Comb=4.
IF ((VarA=0) AND (VarB=1) AND (VarC=1)) Comb=3.
IF ((VarA=0) AND (VarB=1) AND (VarC=0)) Comb=2.
IF ((VarA=0) AND (VarB=0) AND (VarC=1)) Comb=1.
IF ((VarA=0) AND (VarB=0) AND (VarC=0)) Comb=0.
EXECUTE .
 
As usual with my questions, this feels like something that should be obvious.
 
Thanks in advance.
Mike
 
_________________________________________________________________________
Mike Pritchard | [hidden email] | 5 Circles Research | 425-444-3410 (c) | 425-968-3883 (o)
Research to help companies build products that people buy