Filtering terms and variables in R model formulas

f_filter.R

f_filter_vars <- function(formula., ...) {
  f_filter_vars_(formula., .dots = lazyeval::lazy_dots(...))
}

f_filter_vars_ <- function(formula., ..., .dots) {
  dots <- lazyeval::all_dots(.dots, ...)
  .terms <- terms(formula.)
  .factors <- attr(.terms, "factors")
  selectx <- dplyr::select_vars_(rownames(.terms), dots)
  keepx <- as.logical(colSums(attr(ft, "factors")[selectx, , drop = FALSE]))
  dropx <- seq_len(ncol(.factors))[!keepx]
  # this will keep the environment of formula.
  formula(drop.terms(.terms, dropx = dropx))
}

f_filter_terms <- function(formula., ...) {
  f_filter_terms_(formula., .dots = lazyeval::lazy_dots(...))
}

f_filter_terms_ <- function(formula., ..., .dots) {
  dots <- lazyeval::all_dots(.dots, ...)
  .terms <- terms(formula.)
  .factors <- attr(.terms, "factors")
  selectx <- dplyr::select_vars_(colnames(.factors), dots)
  keepx <-  colnames(.factors) %in% selectx
  dropx <- seq_len(ncol(.factors))[!keepx]
  # this will keep the environment of formula.
  formula(drop.terms(.terms, dropx = dropx))
}