R/select-args.R

Defines functions select_args select_args_text

select_args_text <- function(fun, select = "") {
  pieces <- strsplit(select, " +")[[1]]

  tryCatch(
    {
      parsed <- lapply(pieces, function(x) parse(text = x)[[1]])
    },
    error = function(e) {
      stop("Failed to parse: '", select, "'", call. = FALSE)
    }
  )

  select_args(fun, parsed)
}

# Figure out which arguments that the user wants given a function and
# unevaluated list
select_args <- function(fun, select = list()) {
  stopifnot(is.function(fun))
  stopifnot(is.list(select))

  args <- names(formals(fun))
  args <- args[args != "..."]

  if (length(select) == 0) {
    return(args)
  }

  # Construct environment that allow minimal select-style semantics
  arg_idx <- as.list(setNames(seq_along(args), args))
  arg_env <- list2env(arg_idx, parent = emptyenv())
  arg_env$`:` <- `:`
  arg_env$`-` <- `-`
  arg_env$`(` <- `(`

  indices <- lapply(select, eval, envir = arg_env)
  for (i in seq_along(select)) {
    select_check(indices[[i]], select[[i]])
  }

  # If first is negative, start with all vars
  # If first is positive, start with no vars
  select <- rep(select_sign(indices[[1]]) < 0, length(args))

  for (idx in indices) {
    select[abs(idx)] <- select_sign(idx) > 0
  }

  args[select]
}

select_check <- function(x, call) {
  if (is.numeric(x) && (all(x > 0) || all(x < 0)))
    return()

  stop(
    "Arguments must evaluate to all positive or negative numbers.\n",
    "Problem: ", paste(deparse(call), collapse = ""),
    call. = FALSE
  )
}

select_sign <- function(x) {
  if (all(x > 0)) {
    1
  } else if (all(x < 0)) {
    -1
  } else {
    NA
  }
}

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roxygen2 documentation built on Sept. 8, 2021, 9:08 a.m.