str=:; 6e6 $ ,: ('abc', TAB, '12345',LF)
timespacex '(TAB,LF) (e.~ ];._1 ]) LF,str'
0.379227 2.0133e8
On Wed, Dec 10, 2014 at 8:55 AM, Joe Bogner <[email protected]> wrote:
> Brian, thank you. That also works and I hadn't considered it but the
> peformance is not so great on a large string:
>
> timespacex 'str(<@[{&>~([<@:+i.@])/"1@:]) slices'
> 2.44429 6.03512e8
> timespacex '(str ];.0~ ,.)"1 slices'
> 0.385588 3.14331e8
>
> $slices
> 2000000 2
> $str
> 10000000
>
> I don't know if cut ;.3 would help. I don't really understand the nuvoc
> entry or dictionary for it (
> http://www.jsoftware.com/jwiki/Vocabulary/semidot3#dyadic or
> http://www.jsoftware.com/help/dictionary/d331.htm)
>
> It seems like a special case could be written if it doesn't exist for this
> scenario.
>
> Using a 67MB string causes more than 2GB of memory use (out of memory
> error) with :(str ];.0~ ,.)"1 slices ... It's really fast when memory isn't
> an issue, even though it's calling jtcut02 for each row
>
>
> Back to our simple example:
>
> We could write some imperative code that would port well to C:
>
> subarrays2=: 4 : 0
> max=: >./ 1{"1 y
> rows=: {. $ y
> ret=: (rows,max) $ ' '
> row=:0
> for_i. i. rows do.
> 'start len'=: i { y
> col=:0
> for_n. start+i.len do.
> ret=:(n { x) (<row, col) } ret
> col=:>:col
> end.
> row=:>:row
> end.
> ret
> )
>
> str=: 'ab|111*cd|222'
> slices=:(0,2),(3,3),(7,2),:(10,3)
> ](str subarrays2 slices)
> ab
> 111
> cd
> 222
>
>
> This loop has no memory pressure but is extremely slow in J. It completes
> in about 2 minutes on 10 million rows of data. I suspect it would be very
> fast in C since the array can be pre-allocated and two loops.
>
> I could always patch my J binary with it but was wondering if something
> already existed.
>
>
>
>
>
> On Tue, Dec 9, 2014 at 1:27 PM, Brian Schott <[email protected]>
> wrote:
>
> > Joe,
> >
> > Is this relevant?
> >
> > str(<@[{&>~([<@:+i.@])/"1@:]) (0,2),(3,3),(7,2),:(10,3)
> >
> >
> >
> >
> > --
> > (B=)
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
> >
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
