Mailing List Archive: 49091 messages
  • Home
  • Script library
  • AltME Archive
  • Mailing list
  • Articles Index
  • Site search

[REBOL] Transpose Re:

From: joel:neely:fedex at: 6-Oct-2000 8:26

(The following note was written while softly humming, " ... I get by with a little help from my friends, Gonna try with a little help from my friends. ... ) I'm really interested in the idea of a common/shared library of functions/objects such as found on, contained in Ladislav's (as one example of the MANY sites that REBOLlistfolk have), or some of my scribbles earlier in this thread. I'll address the library issue in a follow-up post. As for the function at hand, let me raise a couple of questions: [Al--Bri--xtra--co--nz] wrote:
> Joel wrote: > > Finally, I'd considered handling the structure-traversing > > issues separately from the data-manipulation issues, by > > defining (this version is VERY quick and dirty): > > > >... > > I've cleaned it up a bit: > > ... >
j> transpose: function [b [block!]] [w i s r] [ A> Transpose: function [ A> [catch] A> Transposes Matrices" A> Matrix [block!] A> ][ A> Results Width Height Column A> ][ Nice choice of names (but I MUST remember to ask you about the caps) Since we're discussing, I'll take the liberty to explain my abbrevs as (w)idth (i)ndex (s)ubresult (r)esult :-/ j> r: make block! w: accum length? b/1 map b :length? :min A> Results: make block! Width: length? Matrix/1 A> Height: length? Matrix That bit of obscurity in the initialization of w is explained in a footnote (1) in case I mangled it so badly that no-one can read it. My real question here is this, if we collectively are going to build up a small pile of useful extensions, would it be good to have some conventions re defensive programming, or would that be the sort of thing that should simply be documented (for each) as "possible failure modes"? Alternately, should we have a rating (I do NOT mean "value judgement", but simply accurate labeling of content!) with values such as: "fragile" - "arguments not vetted, you can crash this if you don't play well with others" "robust" - "good faith argument checking done, but there may be some gotchas left" "ironclad" - "we've collectively banged on this one REALLY hard, and are confident that errors will be pre-empted" j> s: make block! length? b A> Column: make block! Width (Boneheaded mistake on my part -- thanks for the correction!) J> foreach c b [append/only s c/:i] j> append/only r s A> foreach Row Matrix [ A> insert/only tail Column Row/:Index A> ] A> insert/only tail Results Column (Sigh... You'd think I'd have learned by now. Thanks for cleaning append/only up into "insert/only tail" -- repeatedly!)
> > Critiques/comments/debugging welcome! > > I totally agree. :-) >
-jn- FOOTNOTE: 1) Regarding the peculiar initialization code r: make block! w: accum length? b/1 map b :length? :min ------1------- -----2----- --------------------3------------------- Step 1 gets the lengths of all sub-blocks in the argument, step 2 assumes the length of the first as a default, and step 3 sets w to the length of the shortest sub-block. This was done so that a collection of (sub-)blocks of different lengths wouldn't cause an error, but would be transposed as far as possible:
>> transpose [[1 2 3 4 5] [1 2 3] [1 2 3 4]]
== [[1 1 1] [2 2 2] [3 3 3]] Of course, this is still not totally robust, as an empty arg block will still not be swallowable (mea culpa!):
>> transpose []
** Script Error: length? expected series argument of type: series port tuple struct. ** Where: r: make block! w: accum This is easy to handle by adding if 0 = length? b [return copy []] to the very beginning of the function, or wrapping the body with either 0 = length? b [ r: copy [] ][ r: ...etc... ...etc... ] r which would then ensure that the basis for accum given by length? b/1 was well-defined. I assume your [catch] was a faster way of addressing this same issue, by simply passing the error resulting from an empty argument list back to the caller. So... should we prefer a style for common/standard library functions, or at least document which position the author (and maintainers) took?