Path: utzoo!news-server.csri.toronto.edu!rutgers!sun-barr!decwrl!csus.edu!ucdavis!caldwr!rfinch
From: rfinch@caldwr.water.ca.gov (Ralph Finch)
Newsgroups: comp.lang.idl-pvwave
Subject: Re: Summary: comparing arrays
Message-ID: <273@locke.water.ca.gov>
Date: 12 Mar 91 18:31:34 GMT
References: <265@locke.water.ca.gov> <271@locke.water.ca.gov>
Organization: Calif. Dept. of Water Resources, Sac.
Lines: 25


Here is yet a fourth way; this technique was mentioned by others.

From: RSI <idl@pprince.Colorado.EDU>

Here is solution #4 (and counting) to your array intersection problem.  The
algorithm is very efficient for byte, integer, and long arrays, that
have a limited range.  It will not work for other data types.

function intersect, a, b
;	Return the values that are common between two arrays.
; Restrictions:
;	A and B should be integers, longs, or bytes.  Their combined range
;	should be relatively small, as two histogram arrays of length equal
;	to the combined range are created.
;
minv = min(a) < min(b)		;Smallest value
return, where((histogram(a, min=minv) ne 0) and $
		(histogram(b, min=minv) ne 0))+minv
end

-- 
Ralph Finch			916-445-0088
rfinch@water.ca.gov		...ucbvax!ucdavis!caldwr!rfinch
Any opinions expressed are my own; they do not represent the DWR