Suppose you wanted to select every fifth case and used the following syntax: One can envision data selection tasks where each case is compared to the last case that passed a similar comparison - there you might leave out the EXECUTE to achieve that strategy.Ī similar situation arise when cases are being selected by original case number in the data set. Placing the EXECUTE before the SELECT IF results in all cases being present when the LAG function is being used. Therefore, case 3 is compared to case 1, rather than case 2, and may be kept or dropped in error. Without an EXECUTE (or other command that forces a data pass) before the SELECT IF, case 2 is evaluated and dropped from the active file before case 3 is evaluated.
Suppose also that case 2 fails the comparison test but case 3 would pass it, i.e., its relation to case 2 is such that you would want to keep case 3. Likewise, you wish to compare case 3 to case 2 and keep or drop case 3 as a result. Suppose you want to keep or drop case 2 depending on the result of a comparison with case 1. To further illustrate the use of EXECUTE among transformations, consider any 3 sequential cases with ID values of 1, 2, and 3. (In this particular example, placing the EXECUTE between the 2 COMPUTES would also work.) Otherwise, when you compute RETURN as DA - LAG(DA) for a given case, the case that originally preceded the current case may have already been dropped from the active file and LAG(DA) may capture the value of DA for an unintended case. What are the rules, in this case and more generally, that dictate when an EXECUTE command should be placed between transformation commands?ĪnswerThe key here was to run EXECUTE before the SELECT IF.
Correct results were obtained if an EXECUTE command was placed somewhere between lines 2 ( Compute RETURN.) and 4 ( SELECT IF.). The results for the variable RETURN were incorrect for some cases.
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