R/anom.prec.R

In jjvanderwal/climates: Methods for working with weather & climate

#define a function to extract anomolies for temperature and precipitaiton
#nc1 & nc2 are current and future (respectively)
#inputs are from retrieve.nc, append.nc or extract.monthly.averages


#' Precipitation Anomoly Calculation
#' 
#' \code{anom.prec} provides a method to estimate the anomoly as a
#' proportionate estimate of the future or past climate relative to the
#' current.
#' 
#' 
#' @param nc1 a list object as created by \code{\link{retrieve.nc}},
#' \code{\link{extract.monthly.average}} or \code{\link{append.nc}}. The
#' minimum set of elements in the list must be dat, lat, lon and tim. See value
#' for a description of these elements.
#' @param nc2 a list object as described in \code{nc1}.
#' @return returns an object that is a list with the same elements as nc1 with
#' the \code{dat} element being the anomoly as a proportion of current.\cr\cr
#' the list will contain at least: \item{dat}{an array containing the anomoly
#' data. The dimensions of the array represent:\cr 1 - time described in this
#' list by \code{tim}\cr 2 - latitude (or y element) described in this list by
#' \code{lat}\cr 3 - longitude (or x element) described in this list by
#' \code{lon}} \item{lat}{vector of latitudes} \item{lon}{vector of longitudes}
#' \item{tim}{vector describing the time element either in e.g., julian days,
#' months or years}
#' @author Jeremy VanDerWal \email{jjvanderwal@@gmail.com}
#' @seealso \code{\link{anom.temp}}, \code{\link{retrieve.nc}},
#' \code{\link{extract.monthly.average}}, \code{\link{append.nc}}
#' @export
#' @examples
#' \dontrun{
#'  ##need to fill in 
#'  }
anom.prec <- 
function(nc1,nc2) { #precipitation of future (nc2) as a proportion of current (nc1)
	#ensure nc1 & nc2 are from retrieve.nc
	if (all(c('dat','tim','lat', 'lon') %in% names(nc1))==FALSE) stop('nc1 must have objects named dat, lat, lon and tim as from retrieve.nc of clim.pact package, append.nc or extract.monthly.averages')
	if (all(c('dat','tim','lat', 'lon') %in% names(nc2))==FALSE) stop('nc2 must have objects named dat, lat, lon and tim as from retrieve.nc of clim.pact package, append.nc or extract.monthly.averages')
	#do the work
	out = nc1; out$dat = nc2$dat / nc1$dat
	class(out) = unique(c(class(out),'nc'))
	return(out)
}