| Cartesian product of a list of lists [message #88500] |
Sun, 04 May 2014 08:48  |
Fabzi
Messages: 305
Registered: July 2010
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Senior Member |
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Folks,
to test all possible parameter combinations for a model run I needed
following algorithm (using lists!):
http://stackoverflow.com/questions/2419370/how-can-i-compute -a-cartesian-product-iteratively
While I was successful in implementing the IDL version of the
*iterative* algorithm (first answer to the above mentioned post), I
miserably failed to implement the *recursive* one. It seems easy but
it's Sunday and I can't figure it out.
Anyway, if someone is interested here's the iterative version. If anyone
wants to try the recursive version I'd be interested to see how it works ;-)
;+
; :Description:
; Computes the Cartesian product of a given number of vectors stored
; in a list. The list can be a list of arrays or a list of lists.
;
; Iterative algorithm obtained here:
; http://stackoverflow.com/questions/2419370/
; how-can-i-compute-a-cartesian-product-iteratively
;
; :Params:
; inList: in, required
; a list of arrays to combine
;
; :Returns:
; a list of arrays with all possible combinations
;
; :Examples:
; Try::
; IDL> l = LIST([1,2,3], [4,5],[6,7])
; IDL> print, w_cartesianProduct(l)
;
; IDL should print::
; 1 4 6
; 1 4 7
; 1 5 6
; 1 5 7
; 2 4 6
; 2 4 7
; 2 5 6
; 2 5 7
; 3 4 6
; 3 4 7
; 3 5 6
; 3 5 7
;
; :Author: Fabien Maussion 2014
; Last modification: FaM, May 4, 2014
;
;-
function w_cartesianProduct, inList
result = list()
nl = inlist.count()
combis = lonarr(nl)
indexes = lonarr(nl)
while 1 do begin
for i=0, nl-1 do combis[i] = (inlist[i])[indexes[i]]
result->add, combis
j = nl - 1
while 1 do begin
indexes[j] += 1
if indexes[j] lt n_elements(inlist[j]) then break
indexes[j] = 0
j -= 1
if j lt 0 then return, result
endwhile
endwhile
end
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