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Topic: Binary or Logical Selection : Given an array A and a binary or
logical vector S, how do I select the rows of A when S = 1 or True ?

Replies: 2   Last Post: Sep 24, 2012 5:36 AM

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 clicliclic@freenet.de Posts: 1,245 Registered: 4/26/08
Re: Binary or Logical Selection : Given an array A and a binary
orlogical vector S, how do I select the rows of A when S = 1 or True ?

Posted: Sep 23, 2012 4:00 PM

Beau Webber schrieb:
>
> Given a 3 column array A of x,y,z numbers, defining a set of spatial
> coordinates, and a binary or logical selection vector S (with as many
> elements as rows in A) :
>
> How do I express the operation of selecting an array R with the set of
> those co-ordinates in A where S is 1 (or true) ?
>
> In Apl I write this as R <- S /[1] A .
>
> But a referee of a paper is asking that I express this in standard
> maths, and I have not yet managed to find an appropriate mathematical
> expression.
> Cheers for any help,
> Beau

I can imagine that referees don't like mathematical explanations in
terms of APL - unless yours is a paper about APL (does the language
still exist?). But I can't think of an elegant way to express this in
standard vector notation either. This newsgroup is only concerned with
the development and application of computer-algebra systems like Maxima
or Maple, I am therefore widening the audience to include sci.math.

Can anybody help the original poster?

Martin.