Re: [Gretl-users] Function to get the powerset
On Thu, 11 Oct 2018, Riccardo (Jack) Lucchetti wrote:
If I'm not mistaken, this is more or less what we came up with in
the end
[...]
Actually, this is slightly faster:
<hansl>
function strings powerset(strings S)
scalar l = nelem(S)
scalar N = 2^l
matrix P = zeros(N,l)
matrix s = seq(0, N-1)'
loop i=1..l --quiet
matrix a = s % 2
matrix P[,i] = a
matrix s = (s-a)/2
endloop
strings PS = array(N)
loop i = 1..N --quiet
string c = ""
loop j = 1..l --quiet
if P[i, j]
c = c ~ " " ~ S[j]
endif
endloop
PS[i] = c
endloop
return PS
end function
</hansl>
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Riccardo (Jack) Lucchetti
Dipartimento di Scienze Economiche e Sociali (DiSES)
Università Politecnica delle Marche
(formerly known as Università di Ancona)
r.lucchetti(a)univpm.it
http://www2.econ.univpm.it/servizi/hpp/lucchetti
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