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Re: Calculating difference between each element in array from previous [message #83807 is a reply to message #83671]

Fri, 29 March 2013 17:07

Phillip Bitzer
Messages: 223
Registered: June 2006

Senior Member

For a start, I think I see where you are differencing adjacent elements of an array. This can be done without looping:

diff = arr - SHIFT(arr, 1)

Note SHIFT will wrap around values, so if that's not important you'll want to "mask" this values somehow.

And then, something like

ind = WHERE(ABS(diff) LE 500., lowCount, NCOMPLEMENT=highCount)

will give you the number of values less than your 500 critical value (lowCount) and greater than 500 (highCount).

I *think* this is what you're asking...

BTW, you should be *very* careful using parentheses to access your array elements. It is much better (safer) to do arr[indices]. There are reasons for this, and a good example of why can be found here:

http://www.idlcoyote.com/misc_tips/imagevarname.php

It is *highly* recommended you get in the habit of putting

compile_opt idl2

in all your routines.

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		Re: Calculating difference between each element in array from previous By: Russell[1] on Fri, 29 March 2013 15:07
		Re: Calculating difference between each element in array from previous By: Phillip Bitzer on Fri, 29 March 2013 17:07

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