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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