[Jprogramming] fixed value of 0 for index origin

Mon Jul 26 09:55:58 HKT 2010

Roger,
When migrating from APL to J there were bigger issues (as in learning new tricks) than index origin. (Like concept of working on items especially with reshape).
I believe that index origin 0 is the "appropriate" choice even though I sometimes get caught up when counting positions in array and then using that constant in J expressions. The brain knows about it but mistakes can happen especially when dealing with inner dimensions. (leading and trailing dimensions I seem to usually get correct - dare I say first and last). The good practice is to set up and use pronouns as indexes, but while it is possible to "strand" scalar numeric constants (as in 3 1 5 { array) pronouns require a verb to combine them ((iSpecies, iID, iSex) { array)
"Appropriate" choice as shown by the following where the index is a calculation from data unrelated to the array being indexed.
(list +./@:(*./ . =) data) { 'missing';'found'
((<data) e. <"1 list) { 'missing';'found'
(16 16 16 16 #: 4011 61453) { '0123456789ABCDEF'
( 3 <. +/ someArray = value) { 'none';'one';'two';'many'
"base" and "plus insert" are two verbs that I like to use for index calculations.
On one major APL project ([]IO <- 1) I worked on as part of a maintenance team I consistently recoded expressions like those above as ARRAY [ []IO + calculation ;] to make plain that the 1 was there only because the calculation yields a result suitable for index origin 0.
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Summary: 0 is the right choice - it make the calculation of indexes cleaner - if there is a constant added then it is there because of other necessities related to the problem. However, because of long time "learning" it is possible to slip up.
Background: mathematics, statistics, computer science.
Current position: statistician
Ian Shannon
Landscape Modelling and Decision Support Section
Department of Environment, Climate Change & Water (NSW)
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On Sat, Jul 24, 2010 at 3:16 PM, Roger Hui <rhui000 at shaw.ca> wrote:
> does the choice of a fixed value of 0 for index origin a
> hindrance to your work?
 
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