R/fuse.R

In avidclam/avidstart: Useful R helper functions for quick start of data analysis projects

#' Merges (fuses) lists recursively
#' 
#' Merges lists so that alike-named elements at the same level of list hierarchy
#' receive the values that come last in the list of arguments.
#' 
#' Side effect of this implementation is that elements get sorted on every level.
#' 
#' @param ... lists to be fused 
#' @return merged list (or vector if arguments are vectors)
#'
#' @examples
#' fuse(1, 2) # Returns 2
#' # Example 1
#' # x = 1 gets replaced by x = list(z = NULL)
#' # y = 0 gets replaced by y = 2
#' fuse(list(y = 0), list(x = 1, y = 2), list(x = list(z = NULL)))
#' # ... and the result equals list(x = list(z = NULL), y = 2)
#' #
#' # Example 2
#' fuse(0, list(NULL), NA, NULL) # yields NA
#' # ... because the last NULL is ignored 
#' # and arguments 0, list(NULL) and NA are fused as unnamed 
#' # and on the same level of list hierarchy
#'
#' @export
fuse <- function(...) {
  arg <- list(...)
  # Get rid of NULLs
  arg <- arg[!sapply(arg, is.null)]
  # Last leaf wins if it's not empty
  la <- length(arg)
  if (la == 0) NULL else if (is_leaf(arg[[la]])) arg[[la]]
  # Drop the leaves, grow named branches
  else {
    flat_arg <- do.call("c", arg[!sapply(arg, is_leaf, simplify = TRUE)])
    lapply(split(flat_arg, get_names(flat_arg)), 
           function(branch) do.call(fuse, unname(branch)))
  }
}