Merge additional variables from a data frame into a Lexis object.
# S3 method for Lexis
merge(x, y, id, by, ...)an object of class Lexis
a data frame
the name of the variable in y to use for matching
against the variable lex.id in x.
if matching is not done by id, a vector of variable names
common to both x and y
optional arguments to be passed to merge.data.frame
A Lexis object with additional columns taken from the
merged data frame.
A Lexis object can be considered as an augmented data frame
in which some variables are time-dependent variables representing
follow-up. The Lexis function produces a minimal object
containing only these time-dependent variables. Additional variables
may be added to a Lexis object using the merge method.