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Re: Unique combinations from a 1d array [message #37699 is a reply to message #37625]

Fri, 16 January 2004 01:43

Chris Lee
Messages: 101
Registered: August 2003

Senior Member

In article <1b881b7a.0401150857.37594317@posting.google.com>, "Darren"
<dapoulio@sympatico.ca> wrote:

> <big snip>
>> return, val[where(y gt 0)]
<snip>

> The total combinations can be found using: n!/(n-p)!*p!
> Where n is the total number of array elements and p is the size of the
> desired combination in my case p = 2. Both of the code examples given
> by Chris do this much more efficiently than what I posted. For 3000
> cases, the matrix approach came in at 0.614s and the loop approach at
> 2.414s on my 2.4 GHz Pentium. However, I believe there was a typo for
> the matrix approach on the last line which should read ï¿½
> return, val[where(mask gt 0)]' to give the array of paired differences.
> Thanks again,
> Darren

Ah,
For the total combinations I just used sum(1..N), which could be replaced
with... (doh, hindsight) N(N-1)/2. Which is the same as yours for p=2 (but
without the 3000 ! )

The typo in the matrix approach....that's what happens when I use
different variables in my IDL code to my newsgroup post :)

Chris.

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[Message index]

		Unique combinations from a 1d array By: dapoulio on Wed, 14 January 2004 14:03
		Re: Unique combinations from a 1d array By: Chris Lee on Fri, 16 January 2004 01:43
		Re: Unique combinations from a 1d array By: dapoulio on Thu, 15 January 2004 08:57

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