These two statements give equivalent results:
3 4{."1&.><arr
and
((<3),(<4)){."1&.><arr
Here's a few exercises which might help:
>3
3
>3 4
3 4
2 *&> 3 4
6 8
<&.>3 4
+---+---+
|+-+|+-+|
||3|||4||
|+-+|+-+|
+---+---+
]"(-&>)
]"0 0 0
I hope this helps.
Thanks,
--
Raul
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
>
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