Subset a variable in a netCDF file

Extracts a subset of a variable from a netCDF file using coordinate bounds supplied for one or more dimensions, and writes the result to a new file.

Usage

nc_subset(
  filename,
  varid,
  output,
  newvarid,
  compression,
  force_v4 = FALSE,
  ...,
  ignore.case = FALSE,
  drop = FALSE
)

Arguments

filename

Character string giving the path to the input netCDF file.

varid

Character string giving the name of the variable to subset. If missing and the file contains a single variable, that variable is used.

output

Character string giving the path to the output netCDF file to create.

newvarid

Optional character string giving the name of the variable in the output file. By default, the original variable name is used.

compression

Optional numeric compression level for the output variable. Supplying this typically requires netCDF4 output.

force_v4

Logical. If `TRUE`, force creation of a netCDF4 output file.

...

Named bounds for dimensions to subset. Each argument name must match a dimension name. Values should be numeric vectors of length two giving lower and upper bounds. A length-one value is treated as an exact coordinate and expanded internally to `c(x, x)`.

ignore.case

Logical. If `TRUE`, ignore case when matching dimension names supplied in `...`.

drop

Logical. If `TRUE`, drop dimensions of length one in the output.

Value

Invisibly returns `output`, or `NULL` invisibly if none of the supplied dimension names match the variable dimensions.

Details

Only dimensions named in `...` are subset; all others are kept in full. The output file contains the subsetted variable, with updated dimension values. Global attributes from the source file are copied to the output file, and the global `history` attribute is updated with the function call.

See also

[nc_extract()], [write_ncdf()]

Examples

if (FALSE) { # \dontrun{
nc_subset(
  filename = "input.nc",
  varid = "temp",
  output = "subset.nc",
  lon = c(-80, -70),
  lat = c(-20, -10),
  depth = c(0, 100)
)
} # }