Abstract
The introduction of hash objects with SAS® version 9 brought about new opportunities for novel programming techniques. The recent discovery that hash tables can contain even other hash objects, also known as the ‘hash of hashes’, opens the door to their application to hierarchical data structures. This is because hierarchies, like the XML structure, can be considered ‘containers within containers’, and with the hash-of-hashes technique, tables can contain tables, thereby becoming compatible with hierarchical formats. This has the potential of being useful for processing clinical data in XML format. The advent of Clinical Data Interchange Standards Consortium (CDISC) and its increasing reliance on XML technology for handling clinical trial data implies that clinical SAS® programmers now have to get used to hierarchical data structures. Clinical trial data set submissions now have to be accompanied by metadata such as define.xml. The traditional SAS® data sets are tabular and relational, whereas the XML structure is hierarchical. SAS® Institute has embraced this new development with a set of XML tools like the XML libname engine, XML mapper, and the CDISC Procedure. One untapped resource is the hash object, which has otherwise proven very useful for fast table look-ups and sortless merges. In this first series of articles, the conversion of a SAS® data set to an XML structure using the hash-of-hashes technique is demonstrated. The illustration is based on a simplified CDISC laboratory data model.
The author is greatly indebted to Dr Paul Dorfman for providing a wealth of information and tutorials about the hashing technique, and for generating so much enthusiasm and ideas for novel applications.
The author also wishes to acknowledge Richard DeVenezia for discovering the hash-of-hashes technique, and providing many elegant examples, making it possible for the author to develop code and produce this paper.
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