I have a large dataset (questionnaire results) of mostly categorical variables. I have tested for dependency between the variables using chi-square test. There are an incomprehensible number of dependencies. I used the chaid() function in the CHAID package to detect interactions and separate out (what I hope to be) the underlying structure of these dependencies for each variable. What typically happens is that the chi-square test will reveal a large number of dependencies (say 10-20) for a variable and the chaid function will reduce this to something much more comprehensible (say 3-5). What I want to do is to extract the names of those variable that were shown to be relevant in the chaid() results.
The chaid() output is in the form of a constparty object. My question is how to extract the variable names associated with the nodes in such an object. Here is a self contained code example: library(evtree) # for the ContraceptiveChoice dataset library(CHAID) library(vcd) library(MASS) data("ContraceptiveChoice") longform <- formula(contraceptive_method_used ~ wifes_education + husbands_education + wifes_religion + wife_now_working + husbands_occupation + standard_of_living_index + media_exposure) z <- chaid(longform, data = ContraceptiveChoice) # plot(z) z # This is the part I want to do programatically shortform <- formula(contraceptive_method_used ~ wifes_education + husbands_occupation) # The thing I want is a programatic way to extract 'shortform' from 'z' # Examples of use of 'shortfom' loglm(shortform, data = ContraceptiveChoice) Thanks in advance Christiaan -- Christiaan Pauw Nova Institute www.nova.org.za ______________________________________________ R-help@r-project.org mailing list 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.