Date: Sep 22, 2012 4:27 PM
Author: dr.beauwebber@googlemail.com
Subject: Binary or Logical Selection : Given an array A and a binary or<br> logical vector S, how do I select the rows of A when S = 1 or True ?

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