#' @title Download and create a data frame of climatology parameters
#'
#' @description This function automates downloading and importing \acronym{CRU}
#' \acronym{CL} v. 2.0 climatology data and creates a data frame of the data.
#' If requested, minimum and maximum temperature may also be automatically
#' calculated as described in the data readme.txt file. Data may be cached for
#' later use by this function, saving time downloading files in future use of
#' the function.
#'
#' Nomenclature and units from readme.txt:
#' \describe{
#' \item{pre}{precipitation (millimetres/month)}
#' \describe{
#' \item{cv}{cv of precipitation (percent)}
#' }
#' \item{rd0}{wet-days (number days with >0.1mm rain per month)}
#' \item{tmp}{mean temperature (degrees Celsius)}
#' \item{dtr}{mean diurnal temperature range (degrees Celsius)}
#' \item{reh}{relative humidity (percent)}
#' \item{sunp}{sunshine (percent of maximum possible (percent of day length))}
#' \item{frs}{ground-frost (number of days with ground-frost per month)}
#' \item{wnd}{10 metre windspeed (metres/second)}
#' \item{elv}{elevation (automatically converted to metres)}
#' }
#' For more information see the description of the data provided by
#' \acronym{CRU}, \url{https://crudata.uea.ac.uk/cru/data/hrg/tmc/readme.txt}
#'
#' @param pre Logical. Fetch precipitation (millimetres/month) from server and
#' return in the data frame? Defaults to \code{FALSE}.
#' @param pre_cv Logical. Fetch cv of precipitation (percent) from server and
#' return in the data frame? Defaults to \code{FALSE}. NOTE. Setting this to
#' \code{TRUE} will always results in \strong{pre} being set to \code{TRUE} and
#' returned as well.
#' @param rd0 Logical. Fetch wet-days (number days with >0.1 millimetres rain
#' per month) and return in the data frame? Defaults to \code{FALSE}.
#' @param dtr Logical. Fetch mean diurnal temperature range (degrees Celsius)
#' and return it in the data frame? Defaults to \code{FALSE}.
#' @param tmp Logical. Fetch temperature (degrees Celsius) and return it in the
#' data frame? Defaults to \code{FALSE}.
#' @param tmn Logical. Calculate minimum temperature values (degrees Celsius)
#' and return it in the data frame? Defaults to \code{FALSE}.
#' @param tmx Logical. Calculate maximum temperature (degrees Celsius) and
#' return it in the data frame? Defaults to \code{FALSE}.
#' @param reh Logical. Fetch relative humidity and return it in the data frame?
#' Defaults to FALSE.
#' @param sunp Logical. Fetch sunshine, percent of maximum possible (percent of
#' day length) and return it in data frame? Defaults to \code{FALSE}.
#' @param frs Logical. Fetch ground-frost records (number of days with ground-
#' frost per month) and return it in data frame? Defaults to \code{FALSE}.
#' @param wnd Logical. Fetch 10m wind speed (metres/second) and return it in the
#' data frame? Defaults to \code{FALSE}.
#' @param elv Logical. Fetch elevation (converted to metres) and return it in
#' the data frame? Defaults to \code{FALSE}.
#' @param cache Logical. Store CRU CL v. 2.0 data files locally for later use?
#' If \code{FALSE}, the downloaded files are removed when R session is closed.
#' To take advantage of cached files in future sessions, use \code{cache = TRUE}
#' after the initial download and caching. Defaults to \code{FALSE}.
#'
#' @examplesIf interactive()
#' # Download data and create a data frame of precipitation and temperature
#' # without caching the data files
#' CRU_pre_tmp <- get_CRU_df(pre = TRUE, tmp = TRUE)
#'
#' head(CRU_pre_tmp)
#' CRU_pre_tmp
#'
#' @seealso
#' \code{\link{create_CRU_stack}}
#' \code{\link{manage_cache}}
#'
#' @return A tidy data frame of \acronym{CRU} \acronym{CL} v. 2.0 climatology
#' elements as a \code{\link[tibble]{tibble}} object
#'
#' @author Adam H. Sparks, \email{adamhsparks@@gmail.com}
#'
#' @note
#' This package automatically converts elevation values from kilometres to
#' metres.
#'
#' @export
get_CRU_df <- function(pre = FALSE,
pre_cv = FALSE,
rd0 = FALSE,
tmp = FALSE,
dtr = FALSE,
reh = FALSE,
tmn = FALSE,
tmx = FALSE,
sunp = FALSE,
frs = FALSE,
wnd = FALSE,
elv = FALSE,
cache = FALSE) {
if (!isTRUE(pre) & !isTRUE(pre_cv) & !isTRUE(rd0) & !isTRUE(tmp) &
!isTRUE(dtr) & !isTRUE(reh) & !isTRUE(tmn) & !isTRUE(tmx) &
!isTRUE(sunp) & !isTRUE(frs) & !isTRUE(wnd) & !isTRUE(elv)) {
stop("\nYou must select at least one element for download.\n",
call. = FALSE)
}
cache_dir <- .set_cache(cache)
files <- .get_CRU(pre,
pre_cv,
rd0,
tmp,
dtr,
reh,
tmn,
tmx,
sunp,
frs,
wnd,
elv,
cache_dir)
return(.create_df(tmn, tmx, tmp, dtr, pre, pre_cv, elv, files))
}
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