| Sum to Arrays [message #4243] |
Thu, 11 May 1995 00:00  |
phrje
Messages: 4
Registered: October 1993
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Junior Member |
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We wish to e.g. sum the columns of a 2d array and store the results in a
1d array. Is there any way to accomplish this without using FOR loops.
Don
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| Re: Sum to Arrays [message #4309 is a reply to message #4243] |
Tue, 23 May 1995 00:00  |
mole
Messages: 5
Registered: April 1995
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Junior Member |
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Stein Vidar Hagfors Haugan (steinhh@amon.uio.no) wrote:
: In article <moleD8uArz.DFG@netcom.com>, mole@netcom.com (Aaron Birenboim) writes:
: [...stuff deleted...]
: |>
: |> OK.... here's a tougher one to vectorize...
: |>
: |>
: |> I want CENTROIDS, FAST!!! I'm stuck with :
: |>
: |> x = fltarr(m)
: |> for i=0,n do x = TOTAL(y(*,i) * findgen(n+1))
: |>
oops... I meant:
x = fltarr(n)
for i=0,n-1 do x(i) = TOTAL(y(*,i) * findgen(m))
get the idea? Weight each column of y by its index and then total
also... I'm trying to be portable between PV-Wave and IDL, so I cannot
use the 2 argument total. (I just found that out)
: Anyway, here are centroids for you:
: Given e.g., I(x,y), an M x N array:
: X = REBIN(REFORM(FINDGEN(M),M,1,/OVERWRITE),M,N,/SAMPLE) ; Gives you X(x,y)
neat. I doubt I'd have come up with that.
: CTROIDS_X = TOTAL(I*X,1)/TOTAL(I,1) ; Gives an array of the centroids
: ; (the X centroid at each y index.)
: CTROID_X = TOTAL(I*X)/TOTAL(I) ; Gives the X Centroid coordinate
: ; of the whole array.
: ;------------ or, for Y centroids...
thanks.
--
Aaron Birenboim | 1007 Pampas Dr. SE |
mole@netcom.com | Albuquerque, NM 87108 |
(505) 254-1749 | |
(505) 247-8371 (w) or birenboi@ataway.aptec.com |
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| Re: Sum to Arrays [message #4336 is a reply to message #4243] |
Sat, 20 May 1995 00:00 |
steinhh
Messages: 260
Registered: June 1994
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Senior Member |
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In article <moleD8uArz.DFG@netcom.com>, mole@netcom.com (Aaron Birenboim) writes:
[...stuff deleted...]
|>
|> OK.... here's a tougher one to vectorize...
|>
|>
|> I want CENTROIDS, FAST!!! I'm stuck with :
|>
|> x = fltarr(m)
|> for i=0,n do x = TOTAL(y(*,i) * findgen(n+1))
|>
|> any ideas???
|>
I don't get it. Why x=fltarr(m), and then set x equal to a scalar n+1
times over? Why findgen(n+1) ?
Anyway, here are centroids for you:
Given e.g., I(x,y), an M x N array:
X = REBIN(REFORM(FINDGEN(M),M,1,/OVERWRITE),M,N,/SAMPLE) ; Gives you X(x,y)
CTROIDS_X = TOTAL(I*X,1)/TOTAL(I,1) ; Gives an array of the centroids
; (the X centroid at each y index.)
CTROID_X = TOTAL(I*X)/TOTAL(I) ; Gives the X Centroid coordinate
; of the whole array.
;------------ or, for Y centroids
Y = REBIN(REFORM(FINDGEN(N),1,N,/OVERWRITE),M,N,/SAMPLE) ; Gives you Y(x,y)
CTROIDS_Y = TOTAL(I*Y,2)/TOTAL(I,2) ; Gives an array of Y centroids...
CTROID_Y = TOTAL(I*Y)/TOTAL(I) ; Gives the Y Centroid.
All vectorized. For some types of applications you should
add something small before dividing with the TOTAL(I,..), to
avoid division with zero, e.g., ...../(TOTAL(I,1)+1e-22)
Stein Vidar
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| Re: Sum to Arrays [message #4342 is a reply to message #4243] |
Fri, 19 May 1995 00:00 |
mole
Messages: 5
Registered: April 1995
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Junior Member |
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Fergus Gallagher (F.Gallagher@nerc.ac.uk) wrote:
: phrje@csv.warwick.ac.uk (Prof. Don McK Paul) wrote:
: >We wish to e.g. sum the columns of a 2d array and store the results in a
: >1d array. Is there any way to accomplish this without using FOR loops.
: >
: >Don
: The total function has an optional second argument, the dimension to sum
: over, e.g.,
: IDL> x = total(y,2)
OK.... here's a tougher one to vectorize...
I want CENTROIDS, FAST!!! I'm stuck with :
x = fltarr(m)
for i=0,n do x = TOTAL(y(*,i) * findgen(n+1))
any ideas???
--
Aaron Birenboim | 1007 Pampas Dr. SE |
mole@netcom.com | Albuquerque, NM 87108 |
(505) 254-1749 | |
(505) 247-8371 (w) or birenboi@ataway.aptec.com |
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