Case Conversion: Mapping and Folding
Dyalog v18.0 introduced ⎕C, which converts the case of characters in an array by mapping to lower case, mapping to upper case, or folding. This superseded an earlier experimental I-beam (819⌶) that could map to lower or upper case but not fold – this I-beam is currently deprecated and will be removed in Dyalog v20.0. […]
Formal Proposal for APL Array Notation – Seeking Feedback
One of the defining features of the APL language is the ability to denote numeric vectors directly through juxtaposition — separating the elements by spaces, as in 0 1 1 2 3 5 8. The notation for character “vectors” is similar to that for “strings” in most other languages, using quotes to denote the start […]
Structural vs. Mathematical "Under"
The APL Farm has recently hosted discussions about the proposed under operator, asking “why Dyalog hasn’t implemented it a long time ago”. I claimed that an important reason was that Roger Hui wasn’t a big fan of the proposed extension known as “structural under”. Stefan Kruger then asked me why that was so. Since Roger […]
Code Golf: Generating Empty Arrays
By: Stefan Kruger Recently, I was looking for a Dyalog problem to pit my wits against, and I asked in the APL Orchard if Adám could make one up: @Adám Any CMCs today? A CMC, if you’re unfamiliar with the APL Orchard, is a Chat Mini Challenge – typically an informal code golf challenge to […]
Towards Improvements to Stencil
Background The stencil operator ⌺ was introduced in Dyalog version 16.0 in 2017. Recently we received some feedback (OK, complaints) that (a) stencil does padding which is unwanted sometimes and needs to be removed from the result and (b) stencil is too slow when it is not supported by special code. First, stencil in cases […]
Ascending and Descending
Lexicographic Ordering Lexicographic ordering is what the APL primitives ⍋ and ⍒ provide: ⎕io←0 ⍝ ⎕io delenda est ⎕rl←7*5 ⍝ to get reproducible random results a←?11 3⍴3 a a ⌷⍨⊂ ⍋a 2 1 0 0 1 0 0 2 2 0 2 2 1 1 1 1 0 0 1 0 0 1 0 1 […]
Dyalog '18 Videos, Week 6
Happy New Year – and Welcome to the 6th week of Dyalog ’18 video releases! If you enjoy geometry, 2019 starts with a couple of real treats; one which builds up to the use of complex numbers just before the end, and another which starts with them and moves on to Quaternions. Alternatively, if you […]
Progressive Index-Of
⎕io=0 is assumed throughout. A recent Forum post motivated investigations into the progressive index-of functions in the FinnAPL Idiom Library: pix ← {((⍴⍺)⍴⍋⍋⍺⍳⍺,⍵) ⍳ ((⍴⍵)⍴⍋⍋⍺⍳⍵,⍺)} ⍝ FinnAPL Idiom 1 pixa ← {((⍋⍺⍳⍺,⍵)⍳⍳⍴⍺) ⍳ ((⍋⍺⍳⍵,⍺)⍳⍳⍴⍵)} ⍝ FinnAPL Idiom 5 In this note, we: explain what is progressive index-of explain why the two functions work investigate the […]
Is it Sorted?
Motivation I have been working on the Dyalog APL quicksort implementation. The following programming puzzle arose in the process of doing the QA for this work. ⍵ is a simple array. Write a function sorted, without using ⍋ or ⍒, such that sorted ⍵ is 1 if ⍵ is sorted in ascending order and 0 […]
Dyadic Grade
⎕io=0 is assumed throughout. The essay talks only about ⍋ but the same ideas apply to ⍒. Background ⍋ has the distinction of being the first (in 1980) APL primitive function defined on major cells: the result orders items of a vector, rows of a matrix, planes of a 3-d array, etc. In the ordering […]
