Hi Jon -
"arr" is boxed because we want to apply "3 4" each to each vector of "arr"
independently of each other. If we think about it, since we're applying
each scalar of the left to each vector on the right, we could try this:
3 4{."(0 1) arr
|length error
| 3 4 {."(0 1)arr
which fails for the stated reason: we're trying to apply two things to ten
things.
On Fri, Sep 26, 2014 at 1:12 PM, Jon Hough <[email protected]> wrote:
> Yes. Thanks. That is what I want, exactly. I just need a little time to
> digest what you've done. I'm not sure why arr is being boxed. Presumably
> under (&.) wants a boxed argument.
> I'm also not sure why your implicit loop, 2 4{."1 , works while mine
> didn't.
> Is there somewhere in the dictionary/NuVoc that explains this?
> I am aware that f&.> is often used to unbox an argument, apply f to the
> result and then box it again. But am not sure how that applies to my
> problem.
>
>
> > Date: Fri, 26 Sep 2014 12:51:03 -0400
> > From: [email protected]
> > To: [email protected]
> > Subject: Re: [Jprogramming] Length errors when getting multiple columns
> from array
> >
> > Not entirely sure what you want, but is this it?
> >
> > 3 4{."1&.><arr
> > +-----+-------+
> > |0 1 2|0 1 2 3|
> > |6 7 8|6 7 8 9|
> > |2 3 4|2 3 4 5|
> > |8 9 0|8 9 0 1|
> > |4 5 6|4 5 6 7|
> > |0 1 2|0 1 2 3|
> > |6 7 8|6 7 8 9|
> > |2 3 4|2 3 4 5|
> > |8 9 0|8 9 0 1|
> > |4 5 6|4 5 6 7|
> > +-----+-------+
> >
> >
> > On Fri, Sep 26, 2014 at 12:44 PM, Jon Hough <[email protected]> wrote:
> >
> > > I have a 2-d array. e.g.
> > > arr =: 10 6 $ i. 10
> > > I want to get the first 3 columns from the array, e.g. 3{."1and get
> the
> > > first 4 elements, e.g. 4{."1
> > > However, combining these, as in
> > > 3 4 {."(0 1) arrgives a length error. Of course 3{. and 4{. will give
> > > different shape results so should be boxed and then concatenated
> > > perhaps(?). I am not sure how to do this, but the end result I want
> would
> > > be something like:
> > >
> > > ┌─────┐
> > >
> > > │0 1 2│
> > >
> > > │6 7 8│
> > >
> > > │2 3 4│
> > >
> > > │8 9 0│
> > >
> > > │4 5 6│
> > >
> > > │0 1 2│
> > >
> > > │6 7 8│
> > >
> > > │2 3 4│
> > >
> > > │8 9 0│
> > >
> > > │4 5 6│
> > >
> > > └─────┘
> > >
> > >
> > > concatenated with
> > >
> > >
> > > ┌───────┐│0 1 2 3││6 7 8 9││2 3 4 5││8 9 0 1││4 5 6 7││0 1 2 3││6 7 8
> 9││2
> > > 3 4 5││8 9 0 1││4 5 6 7│
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > └───────┘
> > >
> > >
> > >
> > > ----------------------------------------------------------------------
> > > For information about J forums see http://www.jsoftware.com/forums.htm
> >
> >
> >
> >
> > --
> > 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
>
--
Devon McCormick, CFA
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
