Changelog

Improve dot handling in model.matrix() method when setting up the terms (reported by Kevin Tappe).

model.part() method tries to avoid calling has_dot() by checking the data attributes first. This can greatly improve speed when there are lots of variables in a model part that is actually not of interest.

Extended processing of formulas with one or more . on the right-hand side: In addition to "separate" and "sequential" processing, there is now dot = "previous" which resolves the . relative to the previous right-hand side part.
model.part() failed in case of variables/terms with very long names. Now deparse(..., width.cutoff = 500) is used to support very long variable names as well.

Enhance Formula() so that if a Formula is supplied it is simply returned unchanged (rather than throwing a warning).
Enhance update() method for Formula object so that also the “new” formula can be a Formula object.

Bug fix for formulas with transformed variables on the left-hand side (e.g., cbind(), log(), or Surv()) and one ore more . on the right-hand side. The terms() and hence the model.frame() now work smoothly. When using model.part() the same Formula (plus dot argument) has to be supplied when preparing the model.frame() and the model.part().

All methods returning formula or Formula objects now preserve the environment of the originally supplied object by default.
The default and formula methods of as.Formula() methods now also take an env argument.

Added a terms = FALSE argument to model.part() method for Formula objects. This can be leveraged when processing multiple offsets. For example for y ~ x + offset(o1) | z + offset(o2). See ?model.part for a worked example.

Package now published in Journal of Statistical Software: doi:10.18637/jss.v034.i01 and citation("Formula") within R.
Added an all.equal() method for Formula objects that produces more intelligible output in case the result is not TRUE.
Fixed an error of the update() method for Formula objects without LHS.

Major revision (not fully backward compatible) to enable support for multiple responses and multiple parts on the right-hand side such as y1 | y2 ~ x, y1 + y2 ~ x1 + x2 | z1, or y ~ u1 + u2 | v1 | x1 + x2 and combinations of these.
Formula objects now consist of the original formula plus two attributes "lhs" and "rhs" that contain the parts of the decomposed left- and right-hand side, respectively.
Most methods take arguments "lhs" and "rhs" which allow selection of the desired parts on the left- and right-hand side respectively, e.g., in a model.frame() or model.matrix().
The previous arguments response = TRUE/FALSE and part = "first"/"second"/"both" were not flexible enough anymore and have been deprecated. Use the streamlined lhs/rhs arguments instead.
vignette("Formula", package = "Formula") illustrates usage of the tools provided by the package and explains the ideas underlying its implementation.
Excluded has.intercept() functionality, rely on standard terms attribute instead.

Added CITATION file.
Added a has.intercept() function with methods for formula and Formula objects.
Change the default value for model.frame.Formula: "both" for a two-part formula and "first" otherwise.

First CRAN release of package Formula for extended formula processing. This package is still under development and the interface might change in future versions.
Currently, this enables processing of formulas such as y ~ x1 + x2 | z1 + z2 + z3 with two parts on the right hand side.
Generalization to further formulas are planned (i.e., not implemented yet), e.g., y1 + y2 ~ x1 + x2 + x3 or y ~ x1 + x2 | u1 | v1 + v2 + v3 | ... i.e., multiple responses and multi-part formulas.

Formula 1.2-6