| array subscripting problem [message #43426] |
Mon, 11 April 2005 06:00  |
m.doyle
Messages: 6
Registered: January 2004
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Junior Member |
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Hi Guys,
I've got a gridded dataset and I'm searching the grid trying to find
those points which have a certain value. Once I've found this point, I
want to check all points around it to see if they have the same value
plus a little bit. This is what I've come up with:
If (data(i,j,k) GE p) THEN begin
cd = data(i,j,k)
If(ABS(cd-data[i-1,j-1,k]) LE mg) then f = f+1
If(ABS(cd-data[i, j-1,k]) LE mg) then f = f+1
If(ABS(cd-data[i+1,j-1,k]) LE mg) then f = f+1
If(ABS(cd-data[i-1,j, k]) LE mg) then f = f+1
If(ABS(cd-data[i+1,j, k]) LE mg) then f = f+1
If(ABS(cd-data[i-1,j+1,k]) LE mg) then f = f+1
If(ABS(cd-data[i, j+1,k]) LE mg) then f = f+1
If(ABS(cd-data[i+1,j+1,k]) LE mg) then f = f+1
endif
However, array subscripting with negative numbers isn't allowed by
IDL.
Has anyone any ideas how I might get around this?
Many thanks!
All the best
Martin
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| Re: array subscripting [message #69145 is a reply to message #43426] |
Fri, 11 December 2009 08:43  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Dave Higgins writes:
> Thanks for your reply. Sorry I wasn't clear in my post. I was
> wondering if there's a better way, in terms of memory management. I.e.
> not creating a second huge array (phi after the rebin), when the
> useful information is a 1d vector.
The IDL Way often involves trade-offs between speed and
memory. A judicious use of a FOR loop might be called
for here, if memory usage is getting ridiculous. But
I would think about transposing your array so that if
you do settle on a loop solution your multiplications
occur on rows of data and not columns of data. Looping
on columns is sure to be slow, slow, slow.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: array subscripting [message #69148 is a reply to message #43426] |
Fri, 11 December 2009 08:29 |
David Higgins
Messages: 13
Registered: August 2009
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Junior Member |
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On 11 Dec, 14:41, David Fanning <n...@dfanning.com> wrote:
> "Easier" in what sense? To type? Make it a function. ;-)
Thanks for your reply. Sorry I wasn't clear in my post. I was
wondering if there's a better way, in terms of memory management. I.e.
not creating a second huge array (phi after the rebin), when the
useful information is a 1d vector.
Thanks.
Dave
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| Re: array subscripting [message #69155 is a reply to message #43426] |
Fri, 11 December 2009 06:41 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Dave Higgins writes:
> I'd like to multiply the 1st dimension of a multi-dimensional array by
> a 1d vector (using * not #). I've been trying to avoid nested FOR
> loops. So far, I've come up with
>
> phi = rebin(phi, dim1,dim2,dim3,dim4,dim5)
> multi_dim_arr = multi_dim_arr * phi
>
> As you can see I'm creating a huge array from a simple "row" of data,
> so that phi and multi_dim_arr match in size. I feel like I'm missing
> something - is there an easier way to get this done?
"Easier" in what sense? To type? Make it a function. ;-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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