Somewhat more efficient (<factor 2) is
((#~ #~ #;.1~@]) 1(0)}a:~:])T
++--+--+--+--+--+---+---+---+---+---+---+--+--+
||Hi|Hi|Hi|Ho|Ho|hee|hee|hee|haw|haw|haw|Yo|Yo|
++--+--+--+--+--+---+---+---+---+---+---+--+--+
Tt=:,5000$,:T
(, 'ratio '; %L:0&}./)100 st &> '((#~ #~ #;.1~@]) 1(0)}a:~:])Tt' ; '(a:&~:
(+/\@[ { {.@] , # ) ]) Tt'
+--------------------------------+----------+------------+----------+
|((#~ #~ #;.1~@]) 1(0)}a:~:])Tt |2758144 |0.0077614099|21407.086 |
+--------------------------------+----------+------------+----------+
|(a:&~: (+/\@[ { {.@] , # ) ]) Tt|3265664 |0.0091752436|29963.263 |
+--------------------------------+----------+------------+----------+
|ratio |0.84458903|0.84590777 |0.71444443|
+--------------------------------+----------+------------+----------+
R.E. Boss
> -----Original Message-----
> From: [email protected] [mailto:programming-
> [email protected]] On Behalf Of Jose Mario Quintana
> Sent: woensdag 7 januari 2015 0:49
> To: Programming forum
> Subject: Re: [Jprogramming] Forward fill w/o looping
>
> "Roger's solution is significantly faster due to the global select."
>
> Indeed, it is leaner too:
>
>
> ( T=. <;._1 ' Hi Ho hee haw Yo ' )
> ┌┬──┬┬┬──┬┬───┬┬┬───┬┬┬──┬┐
> ││Hi│││Ho││hee│││haw│││Yo││
> └┴──┴┴┴──┴┴───┴┴┴───┴┴┴──┴┘
>
> o=. @:
> e=. &.>
>
> st=. (] , < o (1&({::) * 2&({::))) o (] ; 7!:2 o ] ; 6!:2)
> 100 st &> ']`[@.('''' -: ])&.>~/\.&.|. T' ; '(, {~ a:=[)/\.&.|. T' ;
> '(a:&~: (+/\@[ { {.@] , # ) ]) T'
> ┌───────────────────────────────┬─────┬─────────────┬─────
> ───────┐
> │]`[@.('' -: ])&.>~/\.&.|. T │13440│1.77288822e_5│0.238276177 │
> ├───────────────────────────────┼─────┼─────────────┼─────
> ───────┤
> │(, {~ a:=[)/\.&.|. T │8576 │1.84638611e_5│0.158346072 │
> ├───────────────────────────────┼─────┼─────────────┼─────
> ───────┤
> │(a:&~: (+/\@[ { {.@] , # ) ]) T│6016 │9.05480724e_6│0.0544737204│
> └───────────────────────────────┴─────┴─────────────┴─────
> ───────┘
>
>
> I guess versatility does not come cheap, the adverb,
>
> scan=. ((~/)\.)(&.|.)
>
> can be used to perform a series of chained, left-associative, operations,
> while preserving history:
>
> ]`[@.('' -: ])&.>scan T
> ┌┬──┬──┬──┬──┬──┬───┬───┬───┬───┬───┬───┬──┬──┐
> ││Hi│Hi│Hi│Ho│Ho│hee│hee│hee│haw│haw│haw│Yo│Yo│
> └┴──┴──┴──┴──┴──┴───┴───┴───┴───┴───┴───┴──┴──┘
> (,~ {~ a: = ])scan T
> ┌┬──┬──┬──┬──┬──┬───┬───┬───┬───┬───┬───┬──┬──┐
> ││Hi│Hi│Hi│Ho│Ho│hee│hee│hee│haw│haw│haw│Yo│Yo│
> └┴──┴──┴──┴──┴──┴───┴───┴───┴───┴───┴───┴──┴──┘
>
>
> ,. o ((1 % 1 + [)scan o $&1) 33 NB. Golden Section constant...
> 1
> 0.5
> 0.666666667
> 0.6
> 0.625
> 0.615384615
> 0.619047619
> 0.617647059
> 0.618181818
> 0.617977528
> 0.618055556
> 0.618025751
> 0.618037135
> 0.618032787
> 0.618034448
> 0.618033813
> 0.618034056
> 0.618033963
> 0.618033999
> 0.618033985
> 0.61803399
> 0.618033988
> 0.618033989
> 0.618033989
> 0.618033989
> 0.618033989
> 0.618033989
> 0.618033989
> 0.618033989
> 0.618033989
> 0.618033989
> 0.618033989
> 0.618033989
>
> ,. o ((^&(1%3) o (1 + [))scan o $&1) 22 NB. Plastic constant...
> 1
> 1.25992105
> 1.31229384
> 1.32235382
> 1.32426874
> 1.32463263
> 1.32470175
> 1.32471488
> 1.32471737
> 1.32471785
> 1.32471794
> 1.32471795
> 1.32471796
> 1.32471796
> 1.32471796
> 1.32471796
> 1.32471796
> 1.32471796
> 1.32471796
> 1.32471796
> 1.32471796
> 1.32471796
>
> ,. o ((] + % o [)scan) o |. o i. 11 NB. Continued fraction constant
> (right-associative)...
> 10
> 9.1
> 8.10989011
> 7.12330623
> 6.14038425
> 5.16285626
> 4.19369123
> 3.23845342
> 2.30878937
> 1.43312743
> 0.697774658
>
> ,. o ((] + %: o [)scan) o |. o i.22 NB. Nested Radical constant (right
> associative)...
> 21
> 24.5825757
> 23.9580819
> 22.8946994
> 21.7848406
> 20.6674233
> 19.5461438
> 18.4211021
> 17.2919811
> 16.1583628
> 15.0197466
> 13.8755318
> 12.7249875
> 11.56721
> 10.4010601
> 9.22506746
> 8.03727962
> 6.83500963
> 5.61438513
> 4.36946938
> 3.09032758
> 1.75793276
>
> > o (,e/scan) o (":e) o (0.1 , 2 + i.) 22 NB. Champernowne constant
> (formatted)...
> 0.1
> 0.12
> 0.123
> 0.1234
> 0.12345
> 0.123456
> 0.1234567
> 0.12345678
> 0.123456789
> 0.12345678910
> 0.1234567891011
> 0.123456789101112
> 0.12345678910111213
> 0.1234567891011121314
> 0.123456789101112131415
> 0.12345678910111213141516
> 0.1234567891011121314151617
> 0.123456789101112131415161718
> 0.12345678910111213141516171819
> 0.1234567891011121314151617181920
> 0.123456789101112131415161718192021
> 0.12345678910111213141516171819202122
> 0.1234567891011121314151617181920212223
>
>
> One can even play around with an old English formula ;)
>
> 100 ((10x ^ [) <. o * ({: o +: o ((1 + *)scan) o |. o (>: % 1 + 2 * >:) o
> i. o ])) 333x
> 3141592653589793238462643383279502884197169399375105820974944592307
> 8164062862089986280348253421170679
>
>
>
>
>
> On Mon, Jan 5, 2015 at 4:13 PM, Marshall Lochbaum
> <[email protected]>
> wrote:
>
> > Beat me to it by a little. You can tighten it up by not unboxing, and
> > speed up the performance a tiny bit using selection rather than agenda.
> >
> > (, {~ a:=[)/\.&.|.
> >
> > Roger's solution is significantly faster due to the global select.
> >
> > Marshall
> >
> > On Mon, Jan 05, 2015 at 03:15:20PM -0500, Jose Mario Quintana wrote:
> > > ' I'm thinking there's got to be some kind of
> > > loopless prefix sort of solution but am at a loss to come up with it.'
> > >
> > > Maybe it was a suffix, rather than a prefix, solution what you really had
> > > in mind?
> > >
> > > ]`[@.('' -: ])&.>~/\.&.|.
> > >
> > >
> > >
> > > On Mon, Jan 5, 2015 at 11:06 AM, Devon McCormick
> <[email protected]>
> > wrote:
> > >
> > > > I just threw together a short J solution that does what I want but it
> > uses
> > > > a loop and a conditional. I'm thinking there's got to be some kind of
> > > > loopless prefix sort of solution but am at a loss to come up with it.
> > > >
> > > > My code looks like this:
> > > >
> > > > fillEmptyFwd=: 3 : 0
> > > > for_ix. i.<:#y do.
> > > > if. 0=#>y{~>:ix do. y=. (ix{y) (>:ix)}y end.
> > > > end.
> > > > y
> > > > )
> > > >
> > > > An example usage would be this:
> > > >
> > > > fillEmptyFwd '';'Hi';'';'';'Ho';'';'hee';'';'';'haw';'';'';'Yo';''
> > > > ++--+--+--+--+--+---+---+---+---+---+---+--+--+
> > > > ||Hi|Hi|Hi|Ho|Ho|hee|hee|hee|haw|haw|haw|Yo|Yo|
> > > > ++--+--+--+--+--+---+---+---+---+---+---+--+--+
> > > >
> > > > Any ideas on something less loopy/conditional?
> > > >
> > > > --
> > > > Devon McCormick, CFA
> > > > ----------------------------------------------------------------------
> > > > For information about J forums see
> http://www.jsoftware.com/forums.htm
> > > >
> > > ----------------------------------------------------------------------
> > > For information about J forums see
> http://www.jsoftware.com/forums.htm
> > ----------------------------------------------------------------------
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> http://www.jsoftware.com/forums.htm
> >
> ----------------------------------------------------------------------
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