To back up Ber's please have a look at http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example and/or http://adv-r.had.co.nz/Reproducibility.html
John Kane Kingston ON Canada > -----Original Message----- > From: jose.ferr...@logiteng.com > Sent: Wed, 13 Apr 2016 17:18:35 +0000 > To: cdesj...@umn.edu > Subject: Re: [R] reduced set of alternatives in package mlogit > > > > code? example data? We can only guess based on your vague post. > > "PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code." > > Moreover, this sounds like a statistical question, not a question about R > programming, and so might be more appropriate for a statistical list like > stats.stackexchange.com<http://stats.stackexchange.com> . > > Cheers, > Bert > > > Bert Gunter > > > > Sorry if I was not clear enough, but there is hardly any code to show. > The problem is that a parameter or function is lacking (or , mostly > likely, I can't find it), so in some sense the problem itself is that > there is no code to show. > > In what follows choice situations , alternatives, wide, and variables > have the same meaning that they have on the mlogit documentation. All > variables are alternative specific. > > 1)I want to estimate a multinomial Logit using the mlogit package > > 2)I have a dataset, made of choice situations > > 3)There is a set of alternatives > > 4)in some choice situations, not all alternatives were available, but > only a subset of them. So there are no variables for the unavailable > alternatives and the chosen alternative evidently belongs to the set of > available ones. > > 5)I use mlogit.data to prepare the dataset from a "wide" dataframe . > There is no option to have only a subset of alternatives and the > resulting object will have them all , that is, there will be a line for > every alternative and every choice situation, even if in reality some of > them were not available. The variables of these alternatives did not > exist, so must be filled with 0s or any other made up value > > 6) If ones estimate a model from this data it will be wrong > > 7) It is possible to get an "almost right" model by using a dummy > variable marking which alternatives are unavailable, for as it is only > used in alternatives that are never chosen, its coefficient will get > negative with big absolute value, in practice giving almost 0% > probability for them > > 8)this is a workaround because it obligates the model to estimate a > number that should be -infinity and this is known in advance, so it's > ugly and difficult to know what the numeric consequences are as the > coefficient can never converge. In fact, I don't use it the way I > described for these reasons, preferring a more complex but almost > equivalent formulation. The important point is that I want a clean > solution, not a workaround > > 9)I demand simply if mlogit package has such functionality > > > > > > Hi, > I meant that in some choice situations there are some alternatives > missing, but the available alternatives are known to everybody(both the > one that made the choice as well as to who collected the data). > For future reference, I would like to post here that I found the answer. > Apparently it is not possible if one uses mlogit.data with shape = > “wide”, but it is if one uses it with shape = “long” . > So basically one can create an alternative specific variable with > availability (let’s call it is_avaliable) and use mlogit.data normally > that is : > all_avaliable <- mlogit.data(df , shape = “wide” , …) > then one can subset it > real_avaliability <- all_avaliable[all_avaliable$is_avaliable ,] > and resend it through mlogit.data with format long > mlogit.data(real_avaliability , shape = "long" , alt.var = "alt" , > chid.var = "chid", …) > please observe that alt and chid will have been created by the first call > to mlogit.data > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. ____________________________________________________________ TRY FREE IM TOOLPACK at http://www.imtoolpack.com/default.aspx?rc=if5 Capture screenshots, upload images, edit and send them to your friends through IMs, post on Twitter®, Facebook®, MySpace™, LinkedIn® – FAST! ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.