R/process_date.R

In ashiklom/riri: Helper functions for working with Columbia IRI LDEO climate data library

#' Convert NetCDF date to POSIX
#'
#' Try to guess the date unit from the unit string, and use `lubridate` to 
#' convert accordingly.
#'
#' @param nclist NetCDF output as list (see [read_nc2list()])
#' @param remove_original (Logical) Remove original variable from list
#' @export 
process_date <- function(nclist, remove_original = TRUE) {
    if (!"T" %in% names(nclist)) {
        warning("No time variable found in list. Returning original list.")
        return(nclist)
    }
    t_unit <- attr(nclist[["T"]], "units")
    months_since <- grepl("months since", t_unit, ignore.case = TRUE)
    if (months_since) {
        base_date <- lubridate::ymd(t_unit)
        if (is.na(base_date)) {
            warning("Unable to parse date from unit \"", t_unit, "\". Returning original list.")
            return(nclist)
        }
        nclist[["date"]] <- lubridate::`%m+%`(base_date, months(floor(nclist[["T"]]))) +
            lubridate::days(30 * c(nclist[["T"]] %% 1))
        message("Added date column. First few dates are: ",
                paste(head(nclist[["date"]]), collapse = ", "))
        if (remove_original) {
            nclist["T"] <- NULL
        }
    } else {
        warning("Unknown time unit \"", t_unit, "\". Returning original list.")
        return(nclist)
    }
    nclist
}