ynbind column binds a series of related yes/no variables,
allowing for a final argument label used to label the panel
created for the group. labels for individual variables are
collected into a vector attribute "labels" for the result;
original variable names are used in place of labels for those variables
without labels. A positive response is taken to be y, yes,
present (ignoring case) or a logicalTRUE value. By
default, the columns are sorted be ascending order or the overall
proportion of positives. A subsetting method is provided for objects of
class "ynbind".
pBlock creates a matrix similarly labeled, from a general set of
variables (without special handling of binaries), and sets to NA
any observation not in subset so that when that block of
variables is analyzed it will be only for that subset.