Re: [Bug-apl] Implementing Dyalog Key function

[Juergen Sauermann]

Hi Elias, thaks. The explanation is a bit clearer but the problems remain. Key is a non-standard APL function and we should be careful with the implementation of non-standard functions. Every function in GNU APL is an invitation to use it. If the function is obviously useful then it improves the language. If it merely solves a particular programming case, then it may improve GNU APL a little,  but at the price of incompatibility. Programs using it become less portable and that undermines the goal of free software. So the question in such cases is how useful is a function and is that usefulness worth the incompatibility? In the case of the key function I would say no. First of all the key function can only be used if the data it operates on is organized in a specific way: that the first column is the key. That may be the case but the fact that this is needed is somewhat contrary to how other APL function work. You could also call that arbitrary. That goal can easily  achieved by other means. If I have a single KEY then something along the lines of ((DATA[1;]≡KEY)⌿KEY)[1;] will give me the first row (or all rows if I remove the right [1;]) in an array that has that KEY. I suppose that is more or less what the key function does (plus applying some function on that _expression_). The _expression_ is even superior to a function because it can be used at the left side of an assignment. If that is so then the key function is only one of several APL idioms (see http://aplwiki.com/FinnAplIdiomLibrary for a rather famous list of more than 700 such idioms). Each of the 700+  idioms is useful and would deserver its own symbol, but if we would do so (which is technically possible due to Unicode) then we would have turned GNU APL into an unreadable mess. Best Regards, Jürgen Sauermann On 07/03/2017 05:50 AM, Elias Mårtenson wrote: The key function is better described in the Dyalog reference manual, on page 153 here: http://docs.dyalog.com/16.0/Dyalog%20APL%20Language%20Reference%20Guide.pdf Essentially, it's a grouping function. It's used to create groups of similar things, and apply a function on the individual instances. The examples in the section I referenced above should be pretty clear, I think. Regards, Elias On 3 July 2017 at 00:51, Juergen Sauermann <juergen.sauerm...@t-online.de> wrote: Hi Elias, I am not quite in favour of it and it has problems. It is not on my keyboard (even though I am using a Dyalog keyboard). Not to talk about other keyboards. It does not really look like need-to-have function and I suppose it can be efficiently performed by a short combination of other APL primitives. In my opinion adding primitives for every imaginable use case (and there are certainly use cases for the key function) leads to an overloading of the APL language in the long run and does not improve the language. Another problem is that after reading the description several times, I still can't explain in simple terms what the function is actually doing.  That makes it a good candidate for a never used function if it should ever be implemented. Best Regards, Jürgen Sauermann On 07/02/2017 06:24 PM, Elias Mårtenson wrote: How about implementing the key function, ⌸? It's described in this article on the Dyalog site: https://www.dyalog.com/blog/2015/04/exploring-key/ Jürgen, are you in favour of this function? Regards, Elias