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| Re: REVERSE even row elements in data array. [message #12471 is a reply to message #12470] |
Mon, 03 August 1998 00:00  |
Kevin Ivory
Messages: 71
Registered: January 1997
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Member |
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Jouhahn Lee wrote:
> Would you tell me how can I apply REVERSE only to the even row data in
> 64*32 array?
Henry Throop <throop@colorado.edu> already showed you an algorithm
I find confusing. I would do it like this:
data = indgen(64, 32) ; some test data
ydim = (size(data))[2] ; extract number of data rows
rev = indgen(ydim/2) * 2 ; generate the row indexing array
result = data ; only needed if you want to keep original array
result(*, rev) = reverse(data(*, rev), 2) ; reverse every second row
Voila,
Kevin
--
Kevin Ivory Tel: +49 5556 979 434
Max-Planck-Institut fuer Aeronomie Fax: +49 5556 979 240
Max-Planck-Str. 2 mailto:Kevin.Ivory@linmpi.mpg.de
D-37191 Katlenburg-Lindau, GERMANY http://www.gwdg.de/~kivory2/
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| Re: REVERSE even row elements in data array. [message #12475 is a reply to message #12470] |
Sun, 02 August 1998 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Henry Throop (throop2@my-dejanews.com) writes in response
to this question by Jouhahn Lee:
>> Would you tell me how can I apply REVERSE only to the even row data in
>> 64*32 array?
> Try this, with your array to be reversed in the array 'data':
>
> xdim = 64 ; x array dimension
> ydim = 32 ; y array dimension
>
> odds = double(((1+intarr(xdim)) # indgen(ydim)) mod 2)
> ; create a list of integers and a list of 1's,
> ; co-multiply them, and extract last bit.
>
> evens = not odds ; every row of this array which is 1 will be
> ; reversed
>
> result = data*odds + reverse(data*evens)
> ; reverse and extract the appropriate elements
This is very nice. But can you elaborate on why you used
the DOUBLE function in the code above? I get the same result
without it and I am wondering what problem you are trying
to solve by using it.
Thanks for this solution.
David
P.S. I solved the problem in a slightly simpler way, like this:
evens = Indgen(32/2) * 2
data[*, evens] = Reverse( data[*, evens] )
--
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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| Re: REVERSE even row elements in data array. [message #12476 is a reply to message #12475] |
Sun, 02 August 1998 00:00 |
throop2
Messages: 1
Registered: August 1998
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Junior Member |
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In article <35C3E2CB.7F621C0A@maxwell.ph.kcl.ac.uk>,
Jouhahn Lee <jl@maxwell.ph.kcl.ac.uk> wrote:
> Thanks to Mike and Kevin, I could retrieve the microscopic data using
> IDL. Thanks.
>
> Now I can have 64*32 array expandible to 1024* 512 array.
> By the way, in 64*32 array, I need to change the even rows's data
> elements.
> I made a C program for this but I found that subroutine REVERSE in IDL
> can do.
>
> Would you tell me how can I apply REVERSE only to the even row data in
> 64*32 array?
> (ie. keep the odd row, reverse the even row) How can I do that? I am
> still novice using
> IDL so I need to have some help please. Thanks in advance!
When I'm doing things like this, I often create an array of 1's and 0's
to multiply the original array by. This extracts the chosen elements,
and the complement of this array returns all the other, non-chosen elements.
Try this, with your array to be reversed in the array 'data':
xdim = 64 ; x array dimension
ydim = 32 ; y array dimension
odds = double(((1+intarr(xdim)) # indgen(ydim)) mod 2)
; create a list of integers and a list of 1's,
; co-multiply them, and extract last bit.
evens = not odds ; every row of this array which is 1 will be
; reversed
result = data*odds + reverse(data*evens)
; reverse and extract the appropriate elements
- henry
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| Henry Throop throop@colorado.edu (303) 492-1628 |
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| Laboratory for Atmospheric and Space Physics |
| University of Colorado, Boulder 80309-0392 |
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