Dyalog '13: Rank and Friends

Roger Hui

Function rank was first described by Ken Iverson in the 1978 IBM publication Operators and Functions. Its utility was greatly enhanced by the invention of the rank operator by Arthur Whitney in July 1982 and described by Iverson in the I.P. Sharp publication Rationalized APL in January 1983. The rank operator provides for the generalization a function to higher-rank arrays and for its consistent application to lower-rank arrays, and is a simpler alternative to the bracket-axis operator. It also provides a generalization of scalar extension. Version 14.0 adds this powerful tool of thought to Dyalog APL, together with a handful of related features: The key operator which applies the operand function to data grouped according to key values, the tally function, and the extension of index-of to higher rank left arguments. In this presentation, Roger will quickly review the final Version 14.0 specifications for these features, and move on to discussing the benefits of the new features for application programmers.