| Re: For loop avoidance - getting indices of real space [message #81151] |
Mon, 27 August 2012 03:37 |
Yngvar Larsen
Messages: 134
Registered: January 2010
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Senior Member |
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On Thursday, 23 August 2012 22:58:48 UTC+2, simu...@gmail.com wrote:
> I have read and re-read until cross-eyed this post: http://www.idlcoyote.com/tips/forloops.html
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>
>
> And yet, I still can't quite grasp at how I can solve my for loop problem. I think it might involve the use of modulo (MOD), but I'm not sure how. My question is, how can you grab the indices (i,j,k) of a 3D array in real space, and throw them into basically 3 1D arrays that is just a list of all the cells in the "proper" order (column-major).
There is a perfectly good builtin function in IDL to do this: ARRAY_INDICES.
IDL> nx = 15L
IDL> ny = 10L
IDL> nz = 20L
IDL> data = randomn(seed, nx,ny,nz)
IDL> ai = array_indices(data, lindgen(nx*ny*nz))
IDL>
IDL> help, ai
AI LONG = Array[3, 3000]
If you really need dimensions [3000,3], you can add
IDL> ai = transpose(temporary(ai))
--
Yngvar
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| Re: For loop avoidance - getting indices of real space [message #81155 is a reply to message #81151] |
Fri, 24 August 2012 07:41  |
lecacheux.alain
Messages: 325
Registered: January 2008
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Senior Member |
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Le vendredi 24 août 2012 16:25:03 UTC+2, simu...@gmail.com a écrit :
> On Friday, August 24, 2012 5:32:05 AM UTC-4, alx wrote:
>
>> Le jeudi 23 août 2012 22:58:48 UTC+2, simu...@gmail.com a écrit :
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>>
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>> If I understand well your problem, a solution might be:
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>> IDL> coord = [ [lindgen(xcells)#replicate(1,ycells*zcells)], $
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>> IDL> [lindgen(ycells)#replicate(1,xcells*zcells)], $
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>> IDL> [lindgen(zcells)#replicate(1,xcells*ycells)] ]
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>> IDL> coord = reform(coord,ncells,3,/OVER)
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>> alain.
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> This seems like a great idea, but IDL won't let me concatenate arrays like this. The above produces the error message:
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> % Unable to concatenate variables because the dimensions do not agree: <LONG Array[10,300]>.
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> Can you think of another way to form those coordinates?
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> Thanks,
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> Christina
Sorry, I missed one step: I should have rather written:
IDL> coord = [ reform([lindgen(xcells)#replicate(1,ycells*zcells),ncells]), $
IDL> reform([lindgen(ycells)#replicate(1,xcells*zcells)],ncells), $
IDL> reform([lindgen(zcells)#replicate(1,xcells*ycells)],ncells) ]
alain.
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| Re: For loop avoidance - getting indices of real space [message #81157 is a reply to message #81155] |
Fri, 24 August 2012 07:42 |
simulana
Messages: 15
Registered: August 2012
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Junior Member |
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On Friday, August 24, 2012 5:32:05 AM UTC-4, alx wrote:
> Le jeudi 23 août 2012 22:58:48 UTC+2, simu...@gmail.com a écrit :
> If I understand well your problem, a solution might be:
>
>
>
> IDL> coord = [ [lindgen(xcells)#replicate(1,ycells*zcells)], $
>
> IDL> [lindgen(ycells)#replicate(1,xcells*zcells)], $
>
> IDL> [lindgen(zcells)#replicate(1,xcells*ycells)] ]
>
> IDL> coord = reform(coord,ncells,3,/OVER)
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> alain.
Although it may not work exactly as described here, I think I can see a version that would work, albeit less elegantly.
If I just go for each of them individually, like so:
coordx=lindgen(xcells)#replicate(1,ycells*zcells)
coord(ncells,0)=reform(coordx,ncells,1,/OVER)
etc., I think it does work! Thanks!
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| Re: For loop avoidance - getting indices of real space [message #81158 is a reply to message #81155] |
Fri, 24 August 2012 07:25 |
simulana
Messages: 15
Registered: August 2012
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Junior Member |
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On Friday, August 24, 2012 5:32:05 AM UTC-4, alx wrote:
> Le jeudi 23 août 2012 22:58:48 UTC+2, simu...@gmail.com a écrit :
>
> If I understand well your problem, a solution might be:
>
>
>
> IDL> coord = [ [lindgen(xcells)#replicate(1,ycells*zcells)], $
>
> IDL> [lindgen(ycells)#replicate(1,xcells*zcells)], $
>
> IDL> [lindgen(zcells)#replicate(1,xcells*ycells)] ]
>
> IDL> coord = reform(coord,ncells,3,/OVER)
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>
>
> alain.
This seems like a great idea, but IDL won't let me concatenate arrays like this. The above produces the error message:
% Unable to concatenate variables because the dimensions do not agree: <LONG Array[10,300]>.
Can you think of another way to form those coordinates?
Thanks,
Christina
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| Re: For loop avoidance - getting indices of real space [message #81161 is a reply to message #81158] |
Fri, 24 August 2012 02:32 |
lecacheux.alain
Messages: 325
Registered: January 2008
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Senior Member |
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Le jeudi 23 août 2012 22:58:48 UTC+2, simu...@gmail.com a écrit :
> I have read and re-read until cross-eyed this post: http://www.idlcoyote.com/tips/forloops.html
>
>
>
> And yet, I still can't quite grasp at how I can solve my for loop problem. I think it might involve the use of modulo (MOD), but I'm not sure how. My question is, how can you grab the indices (i,j,k) of a 3D array in real space, and throw them into basically 3 1D arrays that is just a list of all the cells in the "proper" order (column-major).
>
>
>
> Here is an example of what I mean:
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> pro testreader
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> xcells=15
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> ycells=10
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> zcells=20
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> ncells=xcells*ycells*zcells
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> data=dindgen(xcells,ycells,zcells)
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> coord=intarr(ncells,3)
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> index=0L
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> for k=0,zcells do begin
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> for j=0,ycells do begin
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> for i = 0,xcells do begin
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> coord(index,0)=i
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> coord(index,1)=j
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> coord(index,2)=k
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> index=index+1
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> endfor
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> endfor
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> endfor
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> end
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> This is a really simple version of a complex problem I have. I have sets of different size boxes from an AMR MHD code, and I need to keep track of their indices, but I just want a list of all of the cells, not to drag around a bunch of smaller arrays or try to concatenate them into one giant sparse array (waste of space). I'm certain that someone must have had this problem before, but I can't find any other suggestions on this forum.
If I understand well your problem, a solution might be:
IDL> coord = [ [lindgen(xcells)#replicate(1,ycells*zcells)], $
IDL> [lindgen(ycells)#replicate(1,xcells*zcells)], $
IDL> [lindgen(zcells)#replicate(1,xcells*ycells)] ]
IDL> coord = reform(coord,ncells,3,/OVER)
alain.
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