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Re: performing multiple histograms without loops [message #69679 is a reply to message #69616]

Wed, 03 February 2010 13:47

JDS
Messages: 94
Registered: March 2009

Member

On Feb 2, 12:25 am, Jeremy Bailin <astroco...@gmail.com> wrote:
> I thought it would be worth expanding on the technique that I used in
> response
> to Ed's question, because it's a very useful one. The basic idea is
> this:
> suppose I want to use HISTOGRAM not on one a single set of N data
> points, but
> independently on multiple (say M) sets each of N data points. The
> simple solution
> is to use a for loop, but if M is large the IDL loop penalty soon
> becomes a problem. Is it possible to avoid a loop?
>
> The answer is yes, and the trick is to modify the data in each of the
> M data
> sets so that they don't overlap, and then use a single HISTOGRAM on
> all
> of them at once.

It's a good method... in fact, you've essentially rediscovered the
algorithm employed by HIST_ND (which itself elaborated on IDL's own
HIST_2D). The M sets of N data points constitute a second dimension
(which don't really need to correspond to physical dimensions of any
sort... they could just be "M different sets numbered 0..M-1"). If
you follow through the dimensional analogy, you can also more easily
extract the "sub-histogram" by dumping the raw output into an
appropriately dimensioned array.

JD

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[Message index]

		Re: performing multiple histograms without loops By: Jeremy Bailin on Thu, 04 February 2010 11:21
		Re: performing multiple histograms without loops By: rogass on Thu, 04 February 2010 04:05
		Re: performing multiple histograms without loops By: JDS on Wed, 03 February 2010 13:47
		Re: performing multiple histograms without loops By: Jeremy Bailin on Wed, 03 February 2010 06:12
		Re: performing multiple histograms without loops By: Jeremy Bailin on Wed, 03 February 2010 05:43
		Re: performing multiple histograms without loops By: Wout De Nolf on Tue, 02 February 2010 02:11
		Re: performing multiple histograms without loops By: MC on Tue, 02 February 2010 01:48

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