| where, or, and loops. There has to be a better way. [message #83474] |
Fri, 08 March 2013 15:47  |
anniebryant@gmail.com
Messages: 16
Registered: March 2009
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Junior Member |
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Please see the below example to demonstrate my problem:
--------------------------------
; This is a large floating point array of river basins
huc = fltarr(4800,4800)
; IDs of the basins I want to extract
NEW = [1102,1103,1104,1105]
; Find where the basins are
pos = where(huc eq NEW[0] or $ ; IS THIS THE ONLY WAY TO FIND THE VALUES IN THE LARGER ARRAY??
huc eq NEW[1] or $
huc eq NEW[2] or $
huc eq NEW[3])
; Create new array and insert basins
key = intarr(4800,4800)
key(pos) = 1
---------------------------------
THe issue here is, what happens when the 'NEW' variable has 300 values in it? Do I have to go through 300 iterations of:
pos = where(huc eq NEW[1] or $
............... or $
huc eq NEW[299])
I hope someone has found a way around this.
Thanks for any ideas you can give!!!
Annie
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| Re: where, or, and loops. There has to be a better way. [message #83564 is a reply to message #83474] |
Fri, 08 March 2013 15:55  |
Jeremy Bailin
Messages: 618
Registered: April 2008
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Senior Member |
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On 3/8/13 5:47 PM, AB wrote:
> Please see the below example to demonstrate my problem:
>
> --------------------------------
>
>
> ; This is a large floating point array of river basins
> huc = fltarr(4800,4800)
>
> ; IDs of the basins I want to extract
> NEW = [1102,1103,1104,1105]
>
> ; Find where the basins are
> pos = where(huc eq NEW[0] or $ ; IS THIS THE ONLY WAY TO FIND THE VALUES IN THE LARGER ARRAY??
> huc eq NEW[1] or $
> huc eq NEW[2] or $
> huc eq NEW[3])
>
> ; Create new array and insert basins
> key = intarr(4800,4800)
>
> key(pos) = 1
> ---------------------------------
>
> THe issue here is, what happens when the 'NEW' variable has 300 values in it? Do I have to go through 300 iterations of:
>
> pos = where(huc eq NEW[1] or $
> ............... or $
> huc eq NEW[299])
>
>
> I hope someone has found a way around this.
>
> Thanks for any ideas you can give!!!
> Annie
>
>
>
>
I like the following paradigm for these. It assumes that new is sorted -
you'll need to pre-sort it otherwise.
pos = WHERE(new[VALUE_LOCATE(new, huc)] eq huc)
-Jeremy.
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| Re: where, or, and loops. There has to be a better way. [message #83568 is a reply to message #83474] |
Fri, 08 March 2013 16:30 |
wlandsman
Messages: 743
Registered: June 2000
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Senior Member |
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It is unnecessary to use the WHERE() function. Instead directly make the position array
key = (huc EQ new[0]) or (huc EQ new[1]) or (hub EQ new[2])
or if you need to loop:
pos = (huc eq new[0])
for i=1,N_elements(new)-1 do pos = pos and (huc EQ new[i])
It might be possible to improve on this by decimating the array (don't test pixels that have already been flagged), but I believe the coding would be considerably more complicated. --Wayne
On Friday, March 8, 2013 6:47:00 PM UTC-5, AB wrote:
> Please see the below example to demonstrate my problem:
>
>
>
> --------------------------------
>
>
>
>
>
> ; This is a large floating point array of river basins
>
> huc = fltarr(4800,4800)
>
>
>
> ; IDs of the basins I want to extract
>
> NEW = [1102,1103,1104,1105]
>
>
>
> ; Find where the basins are
>
> pos = where(huc eq NEW[0] or $ ; IS THIS THE ONLY WAY TO FIND THE VALUES IN THE LARGER ARRAY??
>
> huc eq NEW[1] or $
>
> huc eq NEW[2] or $
>
> huc eq NEW[3])
>
>
>
> ; Create new array and insert basins
>
> key = intarr(4800,4800)
>
>
>
> key(pos) = 1
>
> ---------------------------------
>
>
>
> THe issue here is, what happens when the 'NEW' variable has 300 values in it? Do I have to go through 300 iterations of:
>
>
>
> pos = where(huc eq NEW[1] or $
>
> ............... or $
>
> huc eq NEW[299])
>
>
>
>
>
> I hope someone has found a way around this.
>
>
>
> Thanks for any ideas you can give!!!
>
> Annie
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| Re: where, or, and loops. There has to be a better way. [message #83570 is a reply to message #83474] |
Fri, 08 March 2013 16:22 |
cgguido
Messages: 195
Registered: August 2005
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Senior Member |
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Something like
h=histogram(huc, bin=1, min=1,re=ri)
w=histobin(ri, new)
key[w]=1
On Friday, March 8, 2013 5:47:00 PM UTC-6, AB wrote:
> Please see the below example to demonstrate my problem:
>
>
>
> --------------------------------
>
>
>
>
>
> ; This is a large floating point array of river basins
>
> huc = fltarr(4800,4800)
>
>
>
> ; IDs of the basins I want to extract
>
> NEW = [1102,1103,1104,1105]
>
>
>
> ; Find where the basins are
>
> pos = where(huc eq NEW[0] or $ ; IS THIS THE ONLY WAY TO FIND THE VALUES IN THE LARGER ARRAY??
>
> huc eq NEW[1] or $
>
> huc eq NEW[2] or $
>
> huc eq NEW[3])
>
>
>
> ; Create new array and insert basins
>
> key = intarr(4800,4800)
>
>
>
> key(pos) = 1
>
> ---------------------------------
>
>
>
> THe issue here is, what happens when the 'NEW' variable has 300 values in it? Do I have to go through 300 iterations of:
>
>
>
> pos = where(huc eq NEW[1] or $
>
> ............... or $
>
> huc eq NEW[299])
>
>
>
>
>
> I hope someone has found a way around this.
>
>
>
> Thanks for any ideas you can give!!!
>
> Annie
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