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Merging in SAS

Merging in SAS. These slides show alternatives regarding the merge of two datasets using the IN data set option (check in the SAS onlinedoc > “BASE SAS”, “SAS Language Reference: Dictionary” > “Data step options” > “IN=“

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Merging in SAS

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  1. Merging in SAS • These slides show alternatives regarding the merge of two datasets using the IN data set option (check in the SAS onlinedoc > “BASE SAS”, “SAS Language Reference: Dictionary” > “Data step options” > “IN=“ • In the slides, the red data goes into the merged data set. The greyed out observations are left out.

  2. The perfect merge

  3. Not so perfect (if a or b;)

  4. If a=b; (both datasets contribute)

  5. If a; (must be in dataset A)

  6. If b; (must be in dataset B)

  7. Notes • The examples assume there is a unique identifier. This can be either one variable (ex, CRSP's PERMNO or Compustat's GVKEY) or more than one variable (for example, PERMNO and DATE for a panel dataset). • Assumption: Both data sets are sorted by the unique identifier(s).

  8. Sample code

  9. Typical problems • If both datasets were complete (they both have the same observed units, then the IF statements would be unnecessary; "if a and b" would be equivalent to leaving the statement out altogether) • If you do not have a BY statement (no identifier -- you somehow know that each row of one datasets corresponds to the same one row in the other dataset), the datasets are just "glued" side-by-side. • Common mishaps: the by variables have different formats across datasets, SAS will merge the datasets, but will put a WARNING in the log. Another common mishap is to have variables with the same name (that are not the ID) -- one of the will be overwritten.

  10. References Good references are • http://ftp.sas.com/techsup/download/technote/ts644.html • and a manual called "Combining and modifying SAS data sets: examples", which is in the RC library. It has a lot of example. Unfortunately, it does not exist in an online version (only the code is available, but the explanations are very good).

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