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Re: chunk indexing like [message #69423 is a reply to message #69422]

Sat, 09 January 2010 01:37

rogass
Messages: 200
Registered: April 2008

Senior Member

Hi, Paolo indirectly shows that loops are sometimes not evil ;) I
tried this one:

pro cr_test_chunk_indexing,n=n,verbose=verbose
n= keyword_set(n)? n : [2,3,1,0,5]

if keyword_set(verbose) then print,n

t0=systime(1)
l1=((l=lindgen(((nm=n_elements(n)>(max(n)))),nm) mod nm))[where((l lt
transpose(rebin(n,nm,nm,/sample))))]
print,'CR-Rebin/mod-approach: ',systime(1)-t0,' seconds
for ,',n_elements(n), ' elements'
if keyword_set(verbose) then print,l1

t0=systime(1)
h=histogram(total(n>0,/CUMULATIVE,/int)-1,/
BINSIZE,MIN=0,REVERSE_INDICES=ri )
nh=n_elements(h)
chinkind=ri[0:nh-1]-ri[0]
ind2=where([1,chinkind[1:*]-chinkind[0:nh-2]] ne 0)
l1=lindgen(nh)-ind2[chinkind]
print,'Histogram-approach: ',systime(1)-t0,' seconds for ,',n_elements
(n), ' elements'
if keyword_set(verbose) then print,l1

t0=systime(1)
res=intarr(total(n))
indexarr=findgen(max(n))
i2=0
FOR i=0,n_elements(n)-1 DO BEGIN
IF n[i] GE 1 THEN BEGIN
res[i2:i2+n[i]-1]=indexarr[0:n[i]-1]
i2=i2+n[i]
ENDIF
ENDFOR
print,'Loop-approach: ',systime(1)-t0,' seconds for ,',n_elements(n),
' elements'
if keyword_set(verbose) then print,res

end

...and got this one:

IDL> cr_test_chunk_indexing, n=round(((i=10))*randomu(seed,i)),/
verbose
9 6 3 0 6
1 2 8 7 5
Rebin/mod-approach: 0.00000000 seconds for , 10
elements
0 1 2 3 4
5 6 7 8 0
1 2 3 4 5
0 1 2 0 1
2 3 4 5 0
0 1 0 1 2
3 4 5 6 7
0 1 2 3 4
5 6 0 1 2
3 4
Histogram-approach: 0.00000000 seconds for , 10
elements
0 1 2 3 4
5 6 7 8 0
1 2 3 4 5
0 1 2 -6 -5
-4 -3 -2 -1 -1
-2 -1 -8 -7 -6
-5 -4 -3 -2 -1
-7 -6 -5 -4 -3
-2 -1 0 1 2
3 4
Loop-approach: 0.00000000 seconds for , 10 elements
0 1 2 3 4 5 6 7
8 0 1 2 3 4 5 0
1 2 0 1 2 3 4
5 0 0 1 0 1 2 3
4 5 6 7 0 1 2 3
4 5 6 0 1 2 3
4
IDL> cr_test_chunk_indexing, n=round(((i=100))*randomu(seed,i))
Rebin/mod-approach: 0.0010001659 seconds for , 100
elements
Histogram-approach: 0.00000000 seconds for , 100
elements
Loop-approach: 0.00000000 seconds for , 100 elements
IDL> cr_test_chunk_indexing, n=round(((i=1000))*randomu(seed,i))
Rebin/mod-approach: 0.050000191 seconds for , 1000
elements
Histogram-approach: 0.017000198 seconds for , 1000
elements
Loop-approach: 0.0049998760 seconds for , 1000 elements
IDL> cr_test_chunk_indexing, n=round(((i=10000))*randomu(seed,i))
Rebin/mod-approach: 3.9480000 seconds for , 10000
elements
Histogram-approach: 2.0690000 seconds for , 10000
elements
Loop-approach: 0.46099997 seconds for , 10000 elements

So, sometimes histogram method fails. Loop is here the fastest one and
my one is the slowest but right one without loops.

JD? Any improvements? :)

Regards

CR

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[Message index]

		Re: chunk indexing like By: David Fanning on Sun, 10 January 2010 08:09
		Re: chunk indexing like By: Wout De Nolf on Sun, 10 January 2010 08:05
		Re: chunk indexing like By: David Fanning on Sun, 10 January 2010 07:07
		Re: chunk indexing like By: Wout De Nolf on Sun, 10 January 2010 05:52
		Re: chunk indexing like By: Wout De Nolf on Sun, 10 January 2010 05:09
		Re: chunk indexing like By: Wout De Nolf on Sun, 10 January 2010 04:22
		Re: chunk indexing like By: rogass on Sat, 09 January 2010 11:07
		Re: chunk indexing like By: David Fanning on Sat, 09 January 2010 09:53
		Re: chunk indexing like By: rogass on Sat, 09 January 2010 08:50
		Re: chunk indexing like By: David Fanning on Sat, 09 January 2010 07:10
		Re: chunk indexing like By: rogass on Sat, 09 January 2010 02:15
		Re: chunk indexing like By: rogass on Sat, 09 January 2010 01:37
		Re: chunk indexing like By: pgrigis on Fri, 08 January 2010 08:16
		Re: chunk indexing like By: Wout De Nolf on Fri, 08 January 2010 06:12

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