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Re: Can this be done using array operations instead? [message #66114 is a reply to message #65921]

Thu, 02 April 2009 10:16

Allan Whiteford
Messages: 117
Registered: June 2006

Senior Member

Robin,

robintw wrote:
> Hi,
>
> I'm quite new to IDL and I've written a function to calculate some
> statistics for an image file in ENVI. The function has to be
> calculated for the 3x3 square around every pixel in the image. At the
> moment I'm using a couple of nested for loops to do that - is there a
> way to do it using array operations instead?
>

Probably :).

> What I suppose I'm asking for is a way to call a particular function
> for every element of an array - is that possible. I know it's possible
> to do NewArray = OldArray * 2, which is calling the + function on
> every element of the array, but is there a way to call my user-defined
> function on each element?
>

I think you want to do something slightly more complicated, you want to
call your user defined function on groups of array elements rather than
invididual array elements.

> I can post code if that would help.
>

If you post stand-alone code which does what you want using loops then
chances are someone can point you in the right direction of code which
does it using array operations.

Particularly useful is the ability to do stuff like this:

NewArray = (OldArray[0:n_elements(OldArray)-1] + OldArray[1:*])/2

which will give you the mean between adjacent elements in oldarray
(oldarray assumed to be 1D). Note that you need to worry about what
happens at the edges as soon as you start doing stuff like this. Note
also that the above example is just to illustrate the type of array
techniques you could use.

> Cheers,
>
> Robin

Thanks,

Allan

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[Message index]

		Can this be done using array operations instead? By: robintw on Thu, 02 April 2009 07:34
		Re: Can this be done using array operations instead? By: Jeremy Bailin on Thu, 02 April 2009 14:11
		Re: Can this be done using array operations instead? By: robintw on Thu, 02 April 2009 12:43
		Re: Can this be done using array operations instead? By: robintw on Thu, 02 April 2009 11:58
		Re: Can this be done using array operations instead? By: Jean H. on Thu, 02 April 2009 11:39
		Re: Can this be done using array operations instead? By: robintw on Thu, 02 April 2009 10:38
		Re: Can this be done using array operations instead? By: Allan Whiteford on Thu, 02 April 2009 10:16
		Re: Can this be done using array operations instead? By: robintw on Thu, 02 April 2009 09:26
		Re: Can this be done using array operations instead? By: Juggernaut on Thu, 02 April 2009 08:58

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