added ersst function, fix #96

bumped patch version
returning ncdf4 object from ersst fxn for now

DESCRIPTION

@@ -7,7 +7,7 @@ Description: Client for many 'NOAA' data sources including the 'NCDC' climate
     for 'NOAA' sea ice data, the 'NOAA' severe weather inventory, 'NOAA' Historical
     Observing 'Metadata' Repository ('HOMR') data, 'NOAA' storm data via 'IBTrACS',
     and tornado data via the 'NOAA' storm prediction center.
-Version: 0.4.4.9400
+Version: 0.4.8.9000
 License: MIT + file LICENSE
 Authors@R: c(
     person("Hart", "Edmund", role = "ctb", email = "Edmund.m.hart@gmail.com"),

NAMESPACE

@@ -26,6 +26,7 @@ export(erddap_grid)
 export(erddap_info)
 export(erddap_search)
 export(erddap_table)
+export(ersst)
 export(gefs)
 export(gefs_dimension_values)
 export(gefs_dimensions)

R/ersst.R

@@ -0,0 +1,79 @@
+#' NOAA Extended Reconstructed Sea Surface Temperature (ERSST) data
+#'
+#' @export
+#' @param year (numeric) A year. Must be > 1853. The max value is whatever 
+#' the current year is. Required
+#' @param month A month, character or numeric. If single digit (e.g. 8), we
+#' add a zero in front (e.g., 08). Required
+#' @param ... Curl options passed on to \code{\link[httr]{GET}}. Optional
+#' @return An \code{ncdf4} object for now, may change output later to
+#' perhaps a data.frame. See \pkg{ncdf4} for parsing the output.
+#' @references 
+#' \url{https://www.ncdc.noaa.gov/data-access/marineocean-data/extended-reconstructed-sea-surface-temperature-ersst-v4}
+#' @details NetCDF files are downloaded, stored, and read from the directory given in the 
+#' \code{path} parameter. The default is \code{~/.rnoaa/ersst}, and files are 
+#' saved within whatever that directory is.
+#' 
+#' Files are quite small, so we don't worry about reading in cached data to 
+#' save time, as we do in other functions in this package. 
+#' @examples \dontrun{
+#' # October, 2015
+#' ersst(year = 2015, month = 10)
+#' 
+#' # May, 2015
+#' ersst(year = 2015, month = 5)
+#' ersst(year = 2015, month = "05")
+#' 
+#' # February, 1890
+#' ersst(year = 1890, month = 2)
+#' 
+#' # Process data
+#' library("ncdf4")
+#' res <- ersst(year = 1890, month = 2)
+#' ## varibles
+#' names(res$var)
+#' ## get a variable
+#' ncdf4::ncvar_get(res, "lon_bnds")
+#'
+#' # curl debugging
+#' library('httr')
+#' ersst(year = 2015, month = 10, config=verbose())
+#' }
+ersst <- function(year, month, path = "~/.rnoaa/ersst", overwrite = TRUE, ...) {
+  check4pkg("ncdf4")
+  ff <- ersst_local(path, year, month)
+  dpath <- ersst_GET(make_ersst(year, month), path = ff, overwrite, ...)
+  ncdf4::nc_open(dpath)
+}
+
+make_ersst <- function(year, month) {
+  check_year(year)
+  month <- check_month(month)
+  paste0(".", year, month, ".nc")
+}
+
+ersst_base <- function(ver = "v4") {
+  sprintf("http://www1.ncdc.noaa.gov/pub/data/cmb/ersst/%s/netcdf/ersst.%s", ver, ver)
+}
+
+check_year <- function(x) {
+  if (nchar(x) != 4) stop("year must be a length 4 numeric", call. = FALSE)
+  if (as.numeric(x) < 1854) stop("year must be > 1853", call. = FALSE)
+}
+
+check_month <- function(x) {
+  if (!nchar(x) %in% c(1, 2)) stop("month must be a length 1 or 2 month value", call. = FALSE)
+  if (as.numeric(x) < 1 || as.numeric(x) > 12) stop("month must be a number between 1 and 12", call. = FALSE)
+  if (nchar(x) == 1) paste0("0", x) else x
+}
+
+ersst_GET <- function(dat, path, overwrite, ...) {
+  dir.create(dirname(path), showWarnings = FALSE, recursive = TRUE)
+  res <- GET(paste0(ersst_base(), dat), write_disk(path, overwrite = overwrite), ...)
+  stop_for_status(res)
+  res$request$output$path
+}
+
+ersst_local <- function(path, year, month) {
+  file.path(path, sprintf("%s%s.nc", year, month))
+}