| The IDL way, summing variable sized slices of array. [message #79758] |
Wed, 04 April 2012 01:00  |
d19997919
Messages: 4
Registered: April 2012
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Junior Member |
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Hi,
I've recently been learning how to use REBIN/REFORM etc. to do the heavy lifting rather than loops, (saving me at least an order of magnitude in execution time in some of the code I'm working with). I have a situation now where I don't know if it's possible to completely remove loops so I was hoping someone more experienced could illuminate me.
In essence the problem is that I have a 3D array which I want to reduce to a 2D array by summing over elements of the first dimension. This wouldn't be an issue apart from the fact that the range of elements that I wish to sum over varies depending on the value of the second dimension.
In code what I have at the moment looks a bit like:
d=DBLARR(nt,nl,ne) ;Array of data
t=DBLARR(nt) ; Array of "axis" values
b=DBLARR(nl,2) ;Array of summation limits
p=DBLARR(nl,ne) ; Array of answer
;<<BIT OF CODE TO FILL THESE ARRAYS>>
FOR i=0L,nl-1 DO BEGIN
tmp=TOTAL(d[b[i,0]:b[i,1],i,*],1) ;Sum elements
p[i,*]=tmp/TOTAL(t[b[i,0]:b[i,1]]) ;Store sum divided by sum of axis (i.e. get average value over summation range)
ENDFOR
RETURN,p
Any help will be appreciated,
Note whilst nl is not necessarily large in the cases I'll be looking at, i'm still interesting in "the IDL way" for this as part of my learning!
Thanks,
David
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