I have a problem to which I'd like a beautiful J solution. I know
it's out there. But I can't find it.
The basic problem is a have a bunch of long "paths". Now, I know some
"shortcuts" down these paths. For example, let's say I want to get to
point X:
$ A-B-C-D-E...-X
Now, say I know shortcuts to points E, M, and T, labeled sE, sM, sT,
respectively. I now have several ways to get to point X:
$ A-B-C...-X
$ sE-F-G...-X
$ sM-N-O...-X
$ sT-U-V...-X
What I want is the shortest way to get to X. In this case, I'd choose
the last path, because T is closest to X.
So, given a Nx2 table of shortcut ; path-equivalent-to-shortcut and
a list of target paths, I want the targets shortened as much as
possible (if no reduction is possible, the target remains unchanged).
A concrete example (somewhat) analogous to my problem would be to
provide an inverse to jpath_z_ . The verb takes a shortcut and
resolves it to a fully qualified path. What I want is the opposite:
Given a fully qualified path, it should return the shortest possible
shortcut.
So, provide a dyadic verb shortcut such that:
pathj =: (2 {."1 SYSTEMFOLDERS_j_,USERFOLDERS_j_)&shortcut
eg =: <;._2 noun define
~Classes\plot\jzplot.ijs
~Main\sysenv.ijs
~config\recent.ijs
~user\labs.txt
)
eg -: pathj jpath&.> eg
1
I have included an (ugly, explicit, nested-loop) model of shortcut
in the postscript.
It is important to note that jpath is "eached" but pathj isn't.
(Of course, in the body of the model, each path is treated
independently, but I don't think in a "beautiful" solution that should
be so.)
A lot of paths will be prefixes of others, and having resolved such a
path once, we should be able to reuse that knowledge for an efficient
solution (would M. help here?). Another way of putting it is that
shortcuts can be relative to other shortcuts.
Note also that file systems permit backtracking with "\..", and my
model reflects this. In my real problem however, that's not possible,
so you may feel free to ignore the possibility in your solution (you
can treat shortcuts followed by "..\" as non-viable/infinite length).
But bonus points for generality if you provide for the possibility.
-Dan
PS: Here is a model:
shortcut =: dyad define
r =. 0 $ a:
for_file. y do.
cutfile =. PATHSEP_j_ cut tolower^:IFWIN32 > file
file_candidates =. file
for_nick_dir. x do.
'nick dir' =. nick_dir
cutdir =. PATHSEP_j_ cut tolower^:IFWIN32 dir
a =. i.&0@:=/ cutdir,:cutfile
relative =. (a~:0) # ('~',nick) ; a }. (#cutdir) # <'..'
candidate =. ; }:,(<'\') ,.~ a: -.~ relative , a }. cutfile
file_candidates =. file_candidates , <candidate
end.
r =. r , ({~ [: (i. <./) #&>) file_candidates -. a:
end.
r
)
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