comp.lang.idl-pvwave archive: archive » Re: How to get matching elements of array efficiently

Home » Public Forums » archive » Re: How to get matching elements of array efficiently

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

Re: How to get matching elements of array efficiently [message #69933 is a reply to message #69932]

Tue, 23 February 2010 12:36

penteado
Messages: 866
Registered: February 2018

Senior Member
Administrator

On Feb 23, 5:11 pm, JJ <j...@cornell.edu> wrote:
> I'm looking for an efficient (non-loop) solution to this problem. I
> have two arrays A, B. The elements of A are not necessarily unique,
> nor is A necessarily sorted. I'd like to find all the indices in A
> that match values that occur in B.
>
> For example, if A = [7,1,8,7,8], B = [7,8], the result should be
> [0,2,3,4].
>
> A and B can have many (order millions) of unique values, so I'd rather
> avoid a loop if I can.
>
> Is there any way to do this efficiently?

Are your values integers as in the example? If they are, and if there
are no big gaps in B (the number of elements of B is not much smaller
than max(B)-min(B)), histogram comes to mind:

h=histogram(A,binsize=1,min=min(b),max=max(b),reverse_indice s=ri)
if (max(h) gt 0L) then res=ri[n_elements(h)+1:*] else (deal with the
case of none found in b)

Which would give the result you want in res, but ordered by bin (their
order in B). In this example, res would be [0,3,2,4].

Report message to a moderator

[Message index]

		Re: How to get matching elements of array efficiently By: JJ on Mon, 01 March 2010 11:18
		Re: How to get matching elements of array efficiently By: JJ on Mon, 01 March 2010 10:58
		Re: How to get matching elements of array efficiently By: JDS on Wed, 24 February 2010 14:26
		Re: How to get matching elements of array efficiently By: Jeremy Bailin on Wed, 24 February 2010 06:46
		Re: How to get matching elements of array efficiently By: rogass on Wed, 24 February 2010 00:54
		Re: How to get matching elements of array efficiently By: wlandsman on Tue, 23 February 2010 13:06
		Re: How to get matching elements of array efficiently By: penteado on Tue, 23 February 2010 12:36

Previous Topic:	Intersection of polyline curve and polygon in 3D
Next Topic:	Deconvolving a set of points

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Fri Oct 10 16:19:53 PDT 2025

Total time taken to generate the page: 0.40572 seconds