Hi,
I want to calculate expected likelihood over a 2D discrete
distribution, something like
\sum_k \sum_l p_{kl} L(v_k, v_l)
It is trivial to write a cycle like
for(k in 1:K)
for(l in 1:L)
sum <- sum + p[k,l]*L(v[k], v[l])
But is there a more clever way for R?
Best wishes,
Ott
Dear Ott, At 11:51 AM 12/9/2002 +0100, you wrote:>I want to calculate expected likelihood over a 2D discrete >distribution, something like > >\sum_k \sum_l p_{kl} L(v_k, v_l) > >It is trivial to write a cycle like > >for(k in 1:K) > for(l in 1:L) > sum <- sum + p[k,l]*L(v[k], v[l]) > >But is there a more clever way for R?If the dimensions K and L are the same (isn't that implied by the common vector v?) then how about something like sum(p * outer(v, v, L)). If there are two vectors, say v1 and v2, then sum(p * outer(v1, v2, L)). I hope that this helps, John ----------------------------------------------------- John Fox Department of Sociology McMaster University Hamilton, Ontario, Canada L8S 4M4 email: jfox at mcmaster.ca phone: 905-525-9140x23604 web: www.socsci.mcmaster.ca/jfox -----------------------------------------------------
>>>>> "Ott" == Ott Toomet <otoomet at econ.dk> >>>>> on Mon, 9 Dec 2002 11:51:25 +0100 writes:Ott> Hi, Ott> I want to calculate expected likelihood over a 2D discrete Ott> distribution, something like Ott> \sum_k \sum_l p_{kl} L(v_k, v_l) Ott> It is trivial to write a cycle like Ott> for(k in 1:K) Ott> for(l in 1:L) Ott> sum <- sum + p[k,l]*L(v[k], v[l]) Ott> But is there a more clever way for R? "more clever" meaning "faster", right? Well, this really depends if L(.,.) is vectorized, i.e. when x1 and x2 are vectors of length n, r <- L(x1,x2) is of lenghth n with the proper values? If this is the case, {something like} the following should work: n <- length(v) v1 <- rep(v, n) v2 <- rep(v, each = n) sum(p * L(v1,v2)) ## or L(v2,v1) if it matters Note that above, cbind(v1,v2) is really a (fast no-names) version of expand.grid(v,v) Hoping this helps, Martin Martin Maechler <maechler at stat.math.ethz.ch> http://stat.ethz.ch/~maechler/ Seminar fuer Statistik, ETH-Zentrum LEO C16 Leonhardstr. 27 ETH (Federal Inst. Technology) 8092 Zurich SWITZERLAND phone: x-41-1-632-3408 fax: ...-1228 <><