On Wednesday, March 26, 2014 4:55:41 PM UTC-5, forth...@gmail.com wrote:
> Hi All,
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> I have a peculiar predicament that I am trying to solve...unfortunately, the nature of the problem does not allow me to google it easy, and IDL is not my main programing language.
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> Let's say I have a 3x3x15 array. I use the where command to find certain values in the first 'frame' (third dimension)--note, this is the main stickler, in that I can only search for these values in the first 'frame' as they are not present throughout the whole array.
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> So, the where command spits out three points in example: [2,3,5].
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> Using array_indices with the dimension of the 3x3x15 array, I get the locations of these points, like [[0,2,0],[1,0,0],[1,2,0]]. This is all fine and dandy so far.
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> My problem is that I need to translate these indices to the corresponding points in all of the 'frames'. In other words, I need [[0,2,0],[1,0,0],[1,2,0],[0,2,1],[1,0,1],[1,2,1],[0,2,2],[1, 0,2],[1,2,2],...through all 15 levels of the third dimension].
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> I have found that I can make a loop with the index being the third dimension to accomplish this, or alternatively I can make an array composed of [where command output, where command output + dimension_1*dimension_2*1, where command output + dimension_1*dimension_2*2, etc.]. But the time to complete these increases heavily as the dimensions of my original array increase (800x800x400 in the case of my project).
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> Thus, I am wondering if anyone might have a shortcut that can be accomplished in one statement (since IDL is usually very good with matrices) like theoretically:
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> ORIGINAL_ARRAY=FINDGEN(800,800,400) ; EXAMPLE
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> TEMP=WHERE(ORIGINAL_ARRAY EQ VALUE-ONLY-IN-FIRST-FRAME,CT)
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> TEMP_IND=ARRAY_INDICES(ORIGINAL_ARRAY,TEMP)
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> DATA_ABOVE_WHERE_POINTS=ORIGINAL_ARRAY[[TEMP_IND[0,*],TEMP_I ND[1,*]],*]
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> that yields HELP,DATA_ABOVE_WHERE_POINTS: DOUBLE = ARRAY[CT,400].
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> Obviously the above does not work because of the way IDL indexes (this yields a [CNT,CNT] array). Thanks for viewing and I appreciate any pointers.
I find this simpler, provided you have enough memory to make a copy of your initial array:
; set an array, 4rd dimension is number of frames
a = findgen(3, 3, 15)
;repeat first slice N_z times:
dim=size(a,/dim)
a0=a[*,*,0]
arepeat=rebin(a0, dim)
;Search for values:
w = where(arepeat gt 1.0 and arepeat lt 5.0, count)
:Get coordinates:
xyz = array_indices(a, w)
;I've checked and xyz is identical to Mike's coordinates. For small xy dims the above is faster, for medium and large xy dims Mike's faster.
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