Transcription of Introduction to Hash Tables
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Introduction to Hash Tables
An Introduction to Hash TablesShaun KaufmannFarm Credit CanadaThispresentationwilladdressfourmai nquestions: Whatarehashesandhowdotheywork? Whatyoucanusethemfor? Whatkindofperformancegainscanhashesprovi de? HowdoIusehashesinSAS?AgendaBeforeweintro ducehashes(hashtables),therearethreeconc eptsthatarehelpfultofacilitateunderstand ing: Whatisadatastructure? WhatistheProgramDataVector? Whatisanobjectinregardtoobjectorientedpr ogramming?Before we adatastructureisaparticularwayofstoringa ndorganizingdatainacomputersothatitcanbe usedefficiently. Adatastructurecanbethoughtofasbeingiscon structedfromdatatypes.(numericandcharact er). Thesimplestdatastructureistheone-dimensi onal(linear)array, StructuresOne Dimensional Array Theprogramdatavectorisastorageplaceinmem orythatcontainsallofthevariablesencounte redbythedatastep. Whentheprogramruns,theprogramdatavectorc ontainstheobservationcurrentlybeingproce ssed. data VectorPDV Example Softwareobjectsareconceptuallysimilartor eal-worldobjects.
•Hash Tables are in memory data structures. •Hash Tables can be used for lookups, sorting, merging and to facilitate complex data manipulations by removing the disk I/O associated with frequent query and update statements. •Hash Tables can provide significant performance gains in certain circumstances.
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