Re: More For Loops

[majewski(at)cygnus.uwa.edu.au_stralia]

On 13 Apr 2000 14:56:09 -0500, Craig Markwardt
<craigmnet@cow.physics.wisc.edu> wrote:

Thankyou very much,
This works perfectly, and rather fast too...

For loop - 13.5 seconds
Reform method - 0.45 seconds (just a bit of a difference - when doing
50 or so data sets)

I ended up needing to throw in a couple more reform functions to get
it in the desired form.

my_data = reform(my_data, 2, x_data/2, y_data, /overwrite)
 data_sets_ev = REFORM(my_data[0,*,*])
 data_sets_od = REFORM(my_data[1,*,*])

>
>> majewski@cygnus.uwa.edu.au_stralia writes:
>...
>> > 	for i = 0, (DATA_size[0]/2)-1 do begin
>> > 		for j = 0, DATA_size[1]-1 do begin		
>> > 			Data_sets_ev[i,j] = my_data[(2*i),(2*j)]
>> > 			Data_sets_od[i,j] = my_data[(2*i),(2*j+1)]
>> > 		endfor
>> > 	endfor
>...
>> 
>> Keep in mind that a (2M) x N array can be thought of as a 2 x M x N
>> array -- or an M x N array of pairs.  IDL can reform the first kind of
>> array into the second, and then it's a simple matter of extracting
>> what you want.  The "_ev" is the first of each pair, the "_od" is the
>> second.
>> 
>> my_data = reform(my_data, 2, x_data/2, y_data, /overwrite)
>> 
>> data_sets_ev = my_data[0,*,*]
>> data_sets_od = my_data[1,*,*]
>
>Ah, replying to myself.  I must be getting older.  
>
>I see now that I didn't understand the layout of your original array.
>Your my_data is really a (2*M*2) x N array.  That is, the even and odd
>rows are interleaved.  This is still no problem.  The revised form is:
>
>my_data = reform(my_data,    2,   x_data/4,           2, y_data, /overwrite)
>;                         pair       row   pair of rows   array
>
>data_sets_ev = my_data[0,*,0,*]
>data_sets_od = my_data[0,*,1,*]
>
>In this case it appears that you are only interested in the first of
>each pair of elements, hence the [0,...].
>
>Craig
>
>-- 
>--------------------------------------------------------------------------
>Craig B. Markwardt, Ph.D.         EMAIL:    craigmnet@cow.physics.wisc.edu
>Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
>--------------------------------------------------------------------------

-------------------------
Leon Majewski

Remote Sensing & Satellite Research Group
Curtin University of Technology, Perth, Australia

email: majewski@ses.curtin.edu.au