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An algorithm puzzle [message #60788]

Fri, 13 June 2008 20:43

Y.T.
Messages: 25
Registered: December 2004

Junior Member

Imagine there's a byte-array named "P" that contains only zeros and
ones:

IDL> help,p
P BYTE = Array[5000, 4250]
IDL> print,n_elements(where(p eq 0 or p eq 1))
21250000
IDL> print,5000L*4250
21250000

I am trying to construct a new (lon)array "D" with the same dimensions
as "P" with the following properties:

If P[x,y] eq 0 then D[x,y] = 0 (this part is easy)
If P[x,y] eq 1 then D[x,y] = the smallest distance between {x,y} and a
point in P that is equal to 0

In essence I'd like to know how far each non-zero "pixel" in p is from
a place that is zero (so that I can do statistics on the frequency of
certain distances and such).

I'm currently brute-forcing it with two for-loops where I calculate
the distance between every single element and every single "other"
element and then finding the minimum. Needless to say this takes about
a metric forever and I figured you folks usually have really clever
ideas so I'm throwing this out here to see whether there isn't some
obscure usage of histogram that does exactly what I want...

cordially

Y.T.

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[Message index]

		An algorithm puzzle By: Y.T. on Fri, 13 June 2008 20:43
		Re: An algorithm puzzle By: Jelle on Mon, 16 June 2008 10:47
		Re: An algorithm puzzle By: David Fanning on Mon, 16 June 2008 06:20
		Re: An algorithm puzzle By: Jelle on Mon, 16 June 2008 03:16
		Re: An algorithm puzzle By: David Fanning on Sun, 15 June 2008 21:29

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