comp.lang.idl-pvwave archive: archive » Re: Vector comparison.

Home » Public Forums » archive » Re: Vector comparison.

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Vector comparison. [message #37060 is a reply to message #37059]

Thu, 20 November 2003 06:49

hunter
Messages: 9
Registered: June 2003

Junior Member

Hi,

Thanks, Chris. I came to a similar routine using histogram and a loop. It
may be more practical than the "memory hogging" answer, in my world anyway
:). Although, I'll keep both on hand. If I think of anything better, I'll be
sure to post it.

Thanks to everone forf their help.
Eli

"Christopher Lee" <cl@127.0.0.1> wrote in message
news:20031120.100922.1987231011.27332@buckley.atm.ox.ac.uk.. .
> In article <3fbbc86c$1@rutgers.edu>, "hunter" <elhunter@rci.rutgers.edu>
> wrote:
>
>
>> Hello,
>> These seems to be a fairly simple problem but I'm having difficulty
>> coming up with an elegant solution.
>> Let's say I have two vectors of type integer: A=[0,1,3,3,3,6,7,9,9]
>> B=[3,7]
>> I would like to design a function which returns the indices of all the
>> elements of A which appear in B.
>> i.e.
>> C=get_match(A,B)
>> should return
>> C=[2,3,4,6]
>> The simplest answer (I believe) is to loop through B and use the where
>> command. I just wonder if there is a way to do this without useing the
>> loop, as (in reality) the length of B may be very large. I suppose
>> another possibility is to use the histogram command with reverse_indices
>> set. But I think this would still require me to use a loop. Although it
>> may be faster since I would only have to call histogram once. Any
>> thoughts?
>> Thanks,
>> Eli
>>
>
> How much memory do you have.... (or, to put it another way, loops really
> aren't that bad when n_elements(array) > big_number :)
>
> anyway, the memory hogging non loopy answer.
>
> a=[0,1,3,3,3,6,7,9,9]
> b=[3,7]
>
> ...........
>
> function get_match,a,b
>
> ;needs some up-to-date version of IDL, 5.4 I think.
>
> na=n_elements(a)
> nb=n_elements(b)
>
> ;some checks go here to make sure the world won't explode, an exersice
> ;for the reader.
>
> reb_a=[na,nb]
> ref_a=[na,1]
> reb_b=[na,nb]
> ref_b=[1,nb]
>
> a_temp=rebin(reform(a, ref_a),reb_a)
> b_temp=rebin(reform(b, ref_b),reb_b)
>
> c_temp=a_temp-b_temp
> a_temp=0
> b_temp=0
>
> w=where(c_temp eq 0, count)
>
> c_temp=0
> ;memory...
>
> if( count gt 0) then c=w mod na
> if( count eq 0) then c=-1
>
> return, c
> end
>
> -----
>
> if they are guaranteed to be integer (non-integer histogramming implies a
> fuzzy match doesn't it?) and B is very big :-
>
> hist=histogram(a,reverse_indices=r)
>
> n=n_elements(b)
>
> if(n eq 0) then c=-1
>
> if(n ge 1) then c=r[r[b[0]-min(a)]:r[b[0]+1-min(a)]-1]
>
> ;does this work if b is not an array, something changed between 5.3 and
> ;5.5 but I forget.
>
> if(n gt 1) then for i=1, n-1 do begin
> c=[c,r[r[b[i]-min(a)]:r[b[i]+1-min(a)]-1]]
> endfor
>
> ;this last bit should work....... This still has the loop of course but
> It does grab all of the indices (unlike a UNIQ approach for example) and
> uses less memory ( O(na) instead of O(na*nb) )
>
> ..
>
> I think there must be a better way (a more IDL way), but inspiration
> hasn't hit yet.
>
> Chris.

Report message to a moderator

[Message index]

		Re: Vector comparison. By: JD Smith on Thu, 20 November 2003 11:38
		Re: Vector comparison. By: tam on Thu, 20 November 2003 10:55
		Re: Vector comparison. By: David Fanning on Thu, 20 November 2003 09:55
		Re: Vector comparison. By: Craig Markwardt on Thu, 20 November 2003 09:35
		Re: Vector comparison. By: tam on Thu, 20 November 2003 09:24
		Re: Vector comparison. By: David Fanning on Thu, 20 November 2003 08:52
		Re: Vector comparison. By: Chris[1] on Thu, 20 November 2003 08:08
		Re: Vector comparison. By: David Fanning on Thu, 20 November 2003 08:08
		Re: Vector comparison. By: R.Bauer on Thu, 20 November 2003 07:11
		Re: Vector comparison. By: tam on Thu, 20 November 2003 07:03
		Re: Vector comparison. By: hunter on Thu, 20 November 2003 06:49
		Re: Vector comparison. By: David Fanning on Thu, 20 November 2003 05:40
		Re: Vector comparison. By: R.Bauer on Thu, 20 November 2003 04:02
		Re: Vector comparison. By: Craig Markwardt on Thu, 20 November 2003 02:19
		Re: Vector comparison. By: Chris Lee on Thu, 20 November 2003 02:09
		Re: Vector comparison. By: R.Bauer on Thu, 20 November 2003 01:01
		Re: Vector comparison. By: Craig Markwardt on Thu, 20 November 2003 00:23
		Re: Vector comparison. By: David Fanning on Wed, 19 November 2003 18:05
		Re: Vector comparison. By: R.Bauer on Wed, 19 November 2003 17:50
		Re: Vector comparison. By: Craig Markwardt on Wed, 19 November 2003 15:48
		Re: Vector comparison. By: Pavel Romashkin on Wed, 19 November 2003 16:09

Previous Topic:	Re: IDLWAVE takes over
Next Topic:	Byte Swapping

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sat Oct 11 13:44:37 PDT 2025

Total time taken to generate the page: 0.64028 seconds