R/utils.r

In robertzk/mungebits: mungebits (http://github.com/robertzk/mungebits)

#' Merge two lists and overwrite latter entries with former entries
#' if names are the same.
#'
#' For example, \code{list_merge(list(a = 1, b = 2), list(b = 3, c = 4))}
#' will be \code{list(a = 1, b = 3, c = 4)}.
#' @param list1 list
#' @param list2 list
#' @return the merged list.
#' @export
#' @examples
#' stopifnot(identical(list_merge(list(a = 1, b = 2), list(b = 3, c = 4)),
#'                     list(a = 1, b = 3, c = 4)))
#' stopifnot(identical(list_merge(NULL, list(a = 1)), list(a = 1)))
list_merge <- function(list1, list2) {
  list1 <- list1 %||% list()
  # Pre-allocate memory to make this slightly faster.
  list1[Filter(function(x) nchar(x) > 0, names(list2) %||% c())] <- NULL
  for (i in seq_along(list2)) {
    name <- names(list2)[i]
    if (!identical(name, NULL) && !identical(name, "")) list1[[name]] <- list2[[i]]
    else list1 <- append(list1, list(list2[[i]]))
  }
  list1
}

`%||%` <- function(x, y) if (is.null(x)) y else x

#' @export
except <- function(x) {
  class(x) <- c('except', class(x))
  x
}