#' get matched argument list for a given function

#'

#' extracts and names user-specified arguments according to function defaults

#'

#' @param package the package to use to get the function from

#' @param name the function name

#' @param object the first argument, which may have a class to match functions to

#' @param \dots user arguments to be used for the list

#' @param use.default use different function name other than <function>.default (optional)

#' @param drop boolean for dropping all non-formal args passed in with \dots

#'

#' @keywords internal

function_args <- function(package, name, object, ..., use.default=paste0(name,'.default'), drop=FALSE){

params <- list(...)

if (!missing(object)) {

if (!is.null(names(object)))

params <- append(object, params)

else {

params <- append(list(object), params)

}

} else {

object = c() # replace w/ empty

}

if (length(params) == 0)

return(list())

# // is there a method for this class?

defFun <- getS3method(name,class(object),optional=TRUE) # will be NULL when object is missing

if (is.null(defFun)){

defFun <- getFromNamespace(ifelse(existsFunction(use.default), use.default, name), package)

}

arg.names = names(formals(defFun))[which(!names(formals(defFun)) %in% names(params))]

if (is.null(names(params))){

# // all are unnamed

if (arg.names[seq_len(length(params))][1] == "..."){

# // special case where unnamed args go to ..., and should remain as characters (such as par("usr"))

return(params)

}

names(params) <- arg.names[seq_len(length(params))]

} else {

names(params)[which(names(params) == "")] <- arg.names[seq_len(sum(names(params) == ""))]

}

# // re-order

sort.i <- seq_len(length(params))

match.i <- match(names(params), names(formals(defFun)))

sort.i[!is.na(match.i)] <- match.i[!is.na(match.i)]

params <- params[sort(sort.i, index.return = TRUE)$ix]

if (drop)

params = params[names(params) %in% names(formals(defFun))]

return(params)

}