(,,./|. (B,:~-.B)#"1 X0,:X1 ) -: B}X0,:X1

2006/10/25, Devon McCormick <[EMAIL PROTECTED]>:

This is an idiom - I don't remember where I first saw it:

   B=. 1=2|X0=. 999+ X1=. i.10

   B,X0,:X1
  1    0    1    0    1    0    1    0    1    0
999 1000 1001 1002 1003 1004 1005 1006 1007 1008
  0    1    2    3    4    5    6    7    8    9

   B}X0,:X1
0 1000 2 1002 4 1004 6 1006 8 1008


On 10/24/06, Leigh J. Halliwell <[EMAIL PROTECTED]> wrote:
>
> Thank you, Roger and Cliff.  On my first question I was indeed thinking
of
> the monadic amend.  And Cliff's use of it for my second question is
nice,
> too.  But I'd still like to know how to make the identity/left operator
> work
> one-to one, as per my second question:
>
> "2) X0 and X1 are numeric vectors, and B is a Boolean vector.  They all
> have
> the same length.  I'd like to select from X0 where B is 0, and from X1
> where
> B is 1.  I try the expression: X1 [^:B X0.  But the adverb ^:B wants to
> get
> two-dimensional, i.e., to apply each B to every pair of X1 and X2.  How
> can
> I make J to apply the adverb one-to-one with the arguments?"
>
> Sincerely,
> Leigh
>
>
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
>


--
Devon McCormick
^me^ at acm.
org is my
preferred e-mail
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