R/attributes.R

In NCEAS/arcticdatautils: Utilities for the Arctic Data Center

# Functions for editing metadata attributes


#' Get a data.frame of attributes from a NetCDF object
#'
#' Get a data.frame of attributes from a NetCDF object.
#'
#' @param nc (ncdf4/character) Either a ncdf4 object or a file path.
#'
#' @return (data.frame) A data.frame of the attributes.
#'
#' @export
#'
#' @examples
#' \dontrun{
#' get_ncdf4_attributes("./path/to/my.nc")
#' }
get_ncdf4_attributes <- function(nc) {
  stopifnot(is(nc, "ncdf4") || file.exists(nc))

  if (!requireNamespace("ncdf4")) {
    stop(call. = FALSE,
         "The package 'ncdf4' must be installed to run this function. ",
         "Please install it and try again.")
  }

  # Read the file in if `nc` is a character vector
  if (is.character(nc)) {
    nc <- ncdf4::nc_open(nc)
  }
  dims <- nc$dim


  unitlist <- c()
  for (i in 1:length(dims)) {
    unitlist[i] <- dims[[i]]$units
  }
  inds <- which(unitlist != '')
  dims <- dims[inds]


  attributes <- c(names(nc$var), attributes(dims)$names)

  result <- data.frame(attributeName = NA)

  for (i in seq_along(attributes)) {
    result[i,"attributeName"] <- attributes[i]
    attribute <- ncdf4::ncatt_get(nc, attributes[i])
    att_names <- names(attribute)

    for (name in att_names) {
      if (length(attribute[[name]]) > 1){
        result[i, name] <- paste(attribute[[name]], collapse = ";")
      }
      else if (length(attribute[[name]]) == 1)
        result[i, name] <- attribute[[name]]
    }
  }

  result
}