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Array searching efficiency [message #74959]

Thu, 10 February 2011 15:47

Matt Francis
Messages: 94
Registered: May 2010

Member

Hi All,

I'm going through and trying to squeeze every last bit of optimum
efficiency out of a code I've been working on. I have a small, very
simple, problem that I'd appreciate some experienced input on.

I have a time series of maps, but the time stamps for them are not
always regular (some maps get missed, some are late etc). I need to
(many millions of times..) find which two maps a given time sits
between, then interpolate between the relevant two maps at some given
location.

The first step is to establish, for a given time, which two maps I
need to interpolate between. I have the times for each map stored in a
single array, in time order. If I can work out the indices in that
array of the two map times then I'm done. This is a simple problem to
solve in any number of ways, but the question is which is the fastest?

I've come up with this:

iup = (WHERE(times-time_now GT 0))[0]
ilow = iup-1

I'm not sure how WHERE works 'under the hood', but assuming that at
some level it loops over the given array, then optimally once [times -
time_now] becomes positive you would stop searching. Implementing that
kind of algorithm in a WHILE loop is probably slower than using WHERE
though.

Any thoughts or suggestions?

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[Message index]

		Array searching efficiency By: Matt Francis on Thu, 10 February 2011 15:47
		Re: Array searching efficiency By: pgrigis on Fri, 11 February 2011 07:35
		Re: Array searching efficiency By: Matt Francis on Thu, 10 February 2011 16:47
		Re: Array searching efficiency By: Matt Francis on Thu, 10 February 2011 16:44
		Re: Array searching efficiency By: penteado on Thu, 10 February 2011 16:32
		Re: Array searching efficiency By: David Fanning on Thu, 10 February 2011 16:03

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