Michael Friendly <[EMAIL PROTECTED]> writes: > [Sorry for the re-post; my examples got garbled in the original cut/paste.]
I don't know about then but they sure are now! > Here is a problem that perhaps someone out here has an idea about. It > vaguely reminds me of something > I've seen before, but can't place. Can anyone help? > > For multiple imputation, there are simpler methods available if the > patterns of missing data are 'monotone' --- > if Vj is missing then all variables Vk, k>j are also missing, vs. more > complex methods required when the patterns are not monotone. The > problem is to determine if, for a collection of variables, there is an > ordering of them with a monotone > missing data pattern, or, if not, what the longest monotone sequence > is. Here's my take - no idea about implementation though. You need to draw a directed graph. Nodes are 1...n and the rule is that if Vk is missing in a pattern, you draw an arrow from each j for which Vj is nonmissing, to k. If this graph has no cycles, the collection of patterns is monotone and there is a straightforward method of putting them in order (pick a node with no ancestors, remove it from the graph, repeat). A longest monotone sequence is obtained by finding a maximal cycle-free subgraph. So it all reduces to graph theory. -- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
