as.s2dv_cube() fails if latitude and/or longitude dimensions are not present and length(FileSelectors) > 1

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Hi me,

R and packages Version

R/4.2.1, CSTools

Summary

as.s2dv_cube() fails when the startR_array does not have any dimensions that are in .KnownLatNames() or .KnownLonNames() and there are multiple elements in FileSelectors, because of this piece of code:

    if (length(names(FileSelector)) > 1) {
      # lon name
      known_lon_names <- .KnownLonNames()
      lon_name_dat <- names(dims)[which(names(dims) %in% known_lon_names)]
      # lat name
      known_lat_names <- .KnownLatNames()
      lat_name_dat <- names(dims)[which(names(dims) %in% known_lat_names)]
      result$attrs$Datasets <- names(FileSelector)
      # TO DO: add dat_dim parameter
      if (any(names(dims) %in% c('dat', 'dataset'))) {
        dat_dim <- names(dims)[which(names(dims) %in% c('dat', 'dataset'))]
        result$coords[[dat_dim]] <- names(FileSelector)
        if (!remove_attrs_coords) attr(result$coords[[dat_dim]], 'indices') <- FALSE
      }
      for (i in 2:length(names(FileSelector))) {
        if (!is.null(lon_name_dat)) {
          if (any(result$coords[[lon_name_dat]] != as.vector(attributes(object)$Variables[[names(FileSelector)[i]]][[lon_name_dat]]))) {
            warning("'lon' values are different for different datasets. ", 
                    "Only values from the first will be used.")
          }
        }
        if (!is.null(lat_name_dat)) {
          if (any(result$coords[[lat_name_dat]] != as.vector(attributes(object)$Variables[[names(FileSelector)[i]]][[lat_name_dat]]))) {
            warning("'lat' values are different for different datasets. ", 
                    "Only values from the first will be used.")
          }
        }
      }
    }

If there are no known lat/lon names in names(dims), then names(dims)[which(names(dims) %in% known_lon_names)] returns character(0), not NULL. Therefore !is.null(lat_name_dat) returns FALSE even if lat_name_dat is empty, and the code fails when trying to access result$coords[[lat_name_dat]].

Proposed solution

Changing:

if (!is.null(lon_name_dat)) {
  (...)
}
if (!is.null(lat_name_dat)) {
  (...)
}

To:

if (!length(lon_name_dat) == 0L)) {
  (...)
}
if (!length(lat_name_dat) == 0L)) {
  (...)
}