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Re: Sorting a matrix [message #83475 is a reply to message #83346]

Fri, 08 March 2013 14:24

cgguido
Messages: 195
Registered: August 2005

Senior Member

I was curious to compare this method with a more straightforward way. multisort.pro below does both.
Jeremy's method is twice as fast for large arrays. However, the two methods only give the same result for smallish arrays.

Any ideas what's going on?

;;;;;;;;;;;;;; EXAMPLES ;;;;;;;;;;;;;
multisort, round(randomu(s,20,1e1)*10)
; 1
; 0.00027489662 0.00026106834

multisort, round(randomu(s,20,1e2)*10)
; 0
; 0.00072312355 0.00039005280

;;;;;;;;;;;;;; CODE ;;;;;;;;;;;;;;;
PRO multisort, matrix

compile_opt idl2

matrixshape = size(matrix, /dimen)

t1 = systime(1)

; this gives you the range of each column:
matrixord = lonarr(matrixshape)
for i=0l,matrixshape[0]-1 do matrixord[i,*] = ord(matrix[i,*])
ordmax = max(matrixord, dimen=2)

; what do you need to multiply by to get a unique range?
column_multiply = [reverse(product(reverse(ordmax[1:*]+1), /int, /cumul)), 1]

; create a unique key and sort on it
sortkey = total(matrixord * rebin(column_multiply,matrixshape, /sample), /int, 1)
newmatrix = matrix[*, sort(sortkey)]
t2 = systime(1)

newmatrix2 = matrix
FOR i = matrixshape[0]-1, 0, -1 DO BEGIN
s = bsort(newmatrix2[i, *]);use bsort which maintains order of identical elements
newmatrix2 = newmatrix2[*, s]
ENDFOR
t3 = systime(1)

print,array_equal( newmatrix, newmatrix2)

print, t3-t2, t2-t1

RETURN
END

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[Message index]

		Sorting a matrix By: Mats Löfdahl on Fri, 01 March 2013 04:45
		Re: Sorting a matrix By: Mats Löfdahl on Fri, 01 March 2013 08:49
		Re: Sorting a matrix By: Jeremy Bailin on Tue, 05 March 2013 21:22
		Re: Sorting a matrix By: Jeremy Bailin on Fri, 01 March 2013 08:28
		Re: Sorting a matrix By: Mats Löfdahl on Thu, 07 March 2013 05:32
		Re: Sorting a matrix By: Jeremy Bailin on Thu, 07 March 2013 16:34
		Re: Sorting a matrix By: Mats Löfdahl on Fri, 08 March 2013 16:14
		Re: Sorting a matrix By: cgguido on Fri, 08 March 2013 16:24
		Re: Sorting a matrix By: cgguido on Fri, 08 March 2013 14:24
		Re: Sorting a matrix By: Jeremy Bailin on Fri, 08 March 2013 15:51
		Re: Sorting a matrix By: Mats Löfdahl on Fri, 08 March 2013 16:31

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