netcdf.defVar

Create netCDF variable

Syntax

varid = netcdf.defVar(ncid,varname,xtype,dimids)


Description

varid = netcdf.defVar(ncid,varname,xtype,dimids) creates a new variable in the data set identified by ncid.

• varname is a character vector or string scalar that specifies the name of the variable.

• xtype specifies the NetCDF data type of the variable, using one of these values.

  Value of xtype	MATLAB® Class
  NC_DOUBLE	double
  NC_FLOAT	single
  NC_INT64 (NetCDF-4 files only)	int64
  NC_UINT64 (NetCDF-4 files only)	uint64
  NC_INT	int32
  NC_UINT (NetCDF-4 files only)	uint32
  NC_SHORT	int16
  NC_USHORT (NetCDF-4 files only)	uint16
  NC_BYTE	int8
  NC_UBYTE (NetCDF-4 files only)	uint8
  NC_CHAR	char
  NC_STRING (NetCDF-4 files only)	string

  Alternatively, xtype can be the numeric equivalent returned by the netcdf.getConstant function. For user-defined NC_VLEN types, xtype can be the numeric value returned by the netcdf.defVlen function. NC_VLEN types correspond to cell arrays.

• dimids specifies a list of dimension IDs.

• netcdf.defVar returns varid, a numeric identifier for the new variable.

This function corresponds to the nc_def_var function in the NetCDF library C API. Because MATLAB uses FORTRAN-style ordering, the fastest-varying dimension comes first and the slowest comes last. Any unlimited dimension is therefore last in the list of dimension IDs. This ordering is the reverse of that found in the C API. To use this function, you should be familiar with the NetCDF programming paradigm.

Examples

Define Dimension and Variable in NetCDF File

Create a new NetCDF file, define a dimension in the file, and then define a variable on that dimension. In NetCDF files, you must create a dimension before you can create a variable. To run this example, you must have write permission in your current folder.

Create a new NetCDF file named foo.nc.

ncid = netcdf.create('foo.nc','NC_NOCLOBBER');

Define a dimension in the new file.

dimid = netcdf.defDim(ncid,'x',50);

Define a variable in the new file using netcdf.defVar.

varid = netcdf.defVar(ncid,'myvar','NC_DOUBLE',dimid)

varid = 
0

netcdf.defVar returns a numeric identifier for the new variable.

Close the file.

netcdf.close(ncid)

Tips

• MATLAB interprets data as column major, but the netCDF C API interprets data as row major. Multidimensional data in the netCDF C API shows dimensions in the reverse of the order shown by MATLAB and consequently appears transposed.

Version History

R2022a: Define variable length array data types (NC_VLEN)

You can define variable length array data types (NC_VLEN) in netCDF-4 files.

R2021b: Define NC_STRING data

You can define NC_STRING data in netCDF-4 files.