Some of the rank bits are redundant
arr =: 10 6 $ i. 10
makeMask=: ('' ; 0&,@[ e.~ i.@{:@$@])"0 _
getCols=: {."1@(makeMask <;.1 ])
3 4 getCols arr
┌─────┬───────┐
│0 1 2│0 1 2 3│
│6 7 8│6 7 8 9│
│2 3 4│2 3 4 5│
│8 9 0│8 9 0 1│
│4 5 6│4 5 6 7│
│0 1 2│0 1 2 3│
│6 7 8│6 7 8 9│
│2 3 4│2 3 4 5│
│8 9 0│8 9 0 1│
│4 5 6│4 5 6 7│
└─────┴───────┘
On Sat, Sep 27, 2014 at 1:47 PM, Tikkanz <[email protected]> wrote:
> Here is another alternative using cut:
>
> First build the left arg for cut:
> lhs=: ('' ; 0&,@[ e.~ i.@{:@$@])"0 _
> 3 4 lhs arr
> ┌┬───────────┐
>
> ││1 0 0 1 0 0│
>
> ├┼───────────┤
>
> ││1 0 0 0 1 0│
>
> └┴───────────┘
>
>
> 3 4 ([: {."1 lhs <;.1"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 Sat, Sep 27, 2014 at 1:33 PM, Tikkanz <[email protected]> wrote:
>
>> This becomes easier if you want to extract rows (rather than columns) so
>> one option is to make the columns rows:
>> 3 4 ([: |:&.> [ <@{."0 _ |:@]) 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│
>>
>> └─────┴───────┘
>>
>>
>> Depending on your application it may be worthwhile thinking of changing
>> the format of your array so this isn't necessary.
>>
>>
>> On Sat, Sep 27, 2014 at 5:22 AM, Jon Hough <[email protected]> wrote:
>>
>>> Hi Bob,
>>> What I want is to get certain columns of the array. I know I can use
>>> {."1 to do this. But then I might want to get the first three columns and
>>> also the first 4 columns as the output.I understand that to have my verb
>>> return the first 3 columns and also the first 4 columns, I need to use
>>> boxing. But my problem seems to be in the actual loop {"1, which is the
>>> part I am confused about.I can't do 3 4{"(0 1) arr because the output
>>> shapes are different, but I am sure there is a way to do things like this.
>>>
>>> Your suggestion:
>>> (3&{."1 ; 4&{.) arr
>>> gives what I was after. However if I wanted to get an arbitrary number
>>> of columns, the above becomes unwieldy unless I try something like:
>>> columns =: 3 4 5 4 5 NB. extract the first 3,4,5,4,5 columns respectively
>>> ;/columns{."(0 1) arr
>>> I get a length error trying my above code. Hmm...
>>>
>>> > From: [email protected]
>>> > Date: Fri, 26 Sep 2014 10:03:52 -0700
>>> > To: [email protected]
>>> > Subject: Re: [Jprogramming] Length errors when getting multiple
>>> columns from array
>>> >
>>> > Hi Jon,
>>> >
>>> > I am a bit confused about what you would like as well, but without
>>> boxing you could do this
>>> >
>>> > (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
>>> >
>>> > but I am suspicious of the term 4 elements, so that what you may
>>> really want is this
>>> >
>>> > (3&{."1 ; 4&{.) arr
>>> > ┌─────┬───────────┐
>>> > │0 1 2│0 1 2 3 4 5│
>>> > │6 7 8│6 7 8 9 0 1│
>>> > │2 3 4│2 3 4 5 6 7│
>>> > │8 9 0│8 9 0 1 2 3│
>>> > │4 5 6│ │
>>> > │0 1 2│ │
>>> > │6 7 8│ │
>>> > │2 3 4│ │
>>> > │8 9 0│ │
>>> > │4 5 6│ │
>>> > └─────┴───────────┘
>>> >
>>> > Cheers, bob
>>> >
>>> > On Sep 26, 2014, at 9:51 AM, Devon McCormick <[email protected]>
>>> wrote:
>>> >
>>> > > 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
>>>
>>> ----------------------------------------------------------------------
>>> For information about J forums see http://www.jsoftware.com/forums.htm
>>>
>>
>>
>
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
