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Unique combinations from a 1d array [message #37625]

Wed, 14 January 2004 14:03

dapoulio
Messages: 2
Registered: January 2004

Junior Member

Does anyone know of a more efficient means to determine the set of all
unique combinations of 2 from a 1d array? The following is an approach
that works but for large arrays -say 3000 or more elements it is very
slow. Part of the problem is due to memory because the number of
paired comparisons becomes very large ï¿½ i.e. for 3000 elements the
total number of combinations is 4498500. Writing the paired difference
results to a temporary file helped considerably, but is still far too
slow. Any ideas would be much appreciated.

Here is the code I have:

X = [X1, X2, X3ï¿½..Xn+1]
n = n_elements(X)
d = make_array(1, /float)
for i=0, n-1 do for j=0, n-1 do begin
if i le j then begin
d = [d, X[i] - X[j]]
endif
endfor
d = d[1:n-1]

Thanks in advance,

Darren

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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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