R/infoNcdfAtts.R

In bgctw/ncdfTools: Handling NetCDF Files

infoNcdfAtts <- function(
  ### get summary of all ncdf variable attributes
   file.con   ##<< a NetCDF object pointing to the respective ncdf file.
   , var.id ='NC_GLOBAL'  ##<< the name or id of the variable for which to 
   ## display attributes.
) {
  ##description<< Returns a summary of all attributes of a single variable
  ## in a ncdf file
  ##details<<
  ## If an id or variable name is given for 'var.id ', attributes from one 
  ## variable are returned.
  ## Global attributes are returned if 'NC_GLOBAL' is given. 
  ##seealso<<
  ##\code{\link{infoNcdfDims}}, \code{\link{infoNcdfVars}}
  ##, \code{\link[RNetCDF]{att.inq.nc}}
  if (inherits(file.con, 'character')) {
    if (file.exists(file.con)) {
      file.con =  open.nc(file.con)
      on.exit(close.nc(file.con))
    } else {
      stop(paste('File',  file.con, 'not existent!'))
    }
  }
  n.atts <- if  (var.id == 'NC_GLOBAL') file.inq.nc(file.con)$ngatts else 
     var.inq.nc(file.con,var.id)$natts
  ##value<<
  ## A matrix containing the name, value and type (columns) of 
  ## all attributes (rows)
  att.info <- matrix(NA, n.atts, 3)
  if (n.atts > 0) {
    colnames(att.info)   <- c('name', 'value', 'type')
    for (i in 1:n.atts) {
      attInq <- att.inq.nc(file.con,var.id,i - 1)
      att.info[i,1]    <- attInq$name
      att.values.t     <- att.get.nc(file.con, var.id,i - 1)
      if (length(att.values.t) > 1)
        att.values.t <- paste(att.values.t,collapse = '; ')
      att.info[i,2]    <- att.values.t
      att.info[i,3]    <- attInq$type
    }
    rownames(att.info) <- att.info[,'name']
  }
  return(att.info)
}

infoNcdfAttr <- function(  
  ### get summary of all ncdf variable attributes
  file.con   ##<< a NetCDF object pointing to the respective ncdf file.
  , attr     ##<< string of the attribute name, e.g. "units"
  , var.id ='NC_GLOBAL'  ##<< the name or id of the variable for which to 
  ## get attribute
  , info = infoNcdfAtts(file.con, var.id) ##<< may provide result of
  ## \code{\link{infoNcdfAtts}} for efficiency
) {
  iRow <- match(attr, info[,"name"])
  if (is.na(iRow)) stop("attribute ", attr, " not found for variable ", var.id)
  ##value<< scalar attribute string of first matched attribute
  info[iRow[1],"value"]
}