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Re: chunk indexing like [message #69433 is a reply to message #69423]

Fri, 08 January 2010 08:16

pgrigis
Messages: 436
Registered: September 2007

Senior Member

On Jan 8, 9:12 am, Wox <s...@nomail.com> wrote:
> On Fri, 08 Jan 2010 14:08:45 +0100, Wox <s...@nomail.com> wrote:
>> Hi IDLers,
>
>> I know how to get
>> from [2,3,1,0,5] to [0,0,1,1,1,2,4,4,4,4,4] (i.e. chunk indexing)
>> but how do I get
>> from [2,3,1,0,5] to [0,1,0,1,2,0,0,1,2,3,4]
>> without loops that is.
>
>> I have been juggling with histogram and total(.../cumulative) but I
>> can figure this one out.
>
>> Any ideas?
>
> Ok, I got something working:
>
> n=[2,3,1,0,5]
> 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)
> print,lindgen(nh)-ind2[chinkind]
>
> IDL> 0 1 0 1 2 0 0 1 2 3 4

I wonder how does the IDL-magic version above compares
with the more boring for-loop version below in execution
speed?
I.e. is it worth to go the histogram-way, rewarding
but fraught with danger? ;)

Ciao,
Paolo

n=[2,3,1,0,5]

res=intarr(total(n))
indexarr=findgen(max(n))
i2=0

.run
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
end

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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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