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Data Step Hash Objects as Programming Tools
Koen Vyverman, SAS Netherlands
In SAS® Version 9.1, the hash table - the very first object introduced via the Data Step Component Interface in Version 9.0 - has become robust and syntactically stable. The philosophy and application style of the hash objects differs quite radically from any other structure ever used in the Data step previously. The most notable departure from the tradition is their run-time nature. The hash objects are instantiated and/or deleted and acquire memory, if necessary, at the run-time. It is intuitively clear that such traits should make for very interesting and flexible programming having not seen in the Data step code of yore.
Although some propaedeutics will be provided in the paper, the talk is intended for SAS programmers already somewhat familiar with the basic ideas and syntax behind the hash objects. Instead of teaching hash basics - which by now has been rehashed enough! – live code examples will be used to demonstrate a number of programming techniques, which would be utterly unthinkable before the advent of the canned hash objects in SAS. Imagine using "data _null_" to write a SAS data set, whose name depends on a variable. Or fancy sorting a huge temporary array rapidly and efficiently without the need for sophisticated hand-coding.
In other words, you are in for a few intriguing SAS tunes from the hash land.
- P.Dorfman. Table Lookup by Direct Addressing: Key-Indexing, Bitmapping, Hashing. SUGI 26, Long Beach, CA, 2001.
- P.Dorfman, G.Snell. Hashing Rehashed. SUGI 27, Orlando, FL, 2002.
- D.E.Knuth. The Art of Computer Programming, 3.
- T.Standish. Data Structures, Algorithms & Software Principles in C.
- J.Secosky. The Data step in Version 9: What's New? SUGI 27, Orlando, FL, 2002.
- P.Dorfman, G.Snell. Hashing: Generations. SUGI 28, Seattle, WA, 2003.
- P.Dorfman, K.Vyverman. Hash Component Objects: Dynamic Data Storage and Table Look-Up. SUGI 29, Montreal, 2004.
- P.Dorfman, L.Shajenko. Data Step Programming Using the Hash Objects, NESUG 2004, Baltimore, MD 2004.