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loopsvectorspss

compute sum vector variable in loop - spss syntax

I have a variable A and I would like to subtract all the 1001 elements of this variable as follows: B[n] = A[n+1] - A[n] using spss syntax.

My code:

compute ctord = $casenum .
vector tot(1001).
vector B(1001).
compute tot(ctord) = A.
execute.

loop #i = 1 to 1001.
compute B(#i)=tot(#i+1)-tot(#i).
end loop.

But this code is not working in the loop.

Solution

  • For creating the Variable B[n] = A[n+1] - A[n], where n is your case number, you first need to compute A[n+1] as a new variable:

    CREATE
/A_lead = LEAD(A,1).

    Then you can compute B easily with:

    COMPUTE B = A_lead - A.
EXECUTE.

    After that, you can delete A_lead if you want to.

    DELETE VARIABLES a_lead.