change variable data type from a NetCDF file

I've got a NetCDF file that has many different variables that are int16, int32 and single and I want to convert them to chars or strings.

How could I do it.

Answer 1

[Rupesh]

Hi flashpode,

I understand that you have a NetCDF file containing a range of variables with different data types, specifically variables stored as int16, int32, and single (floating-point). You want to convert the values of these variables from their original numeric data types into characters or strings.

To achieve this, you can follow the below steps.

• Open the “NetCDF” file using MATLAB functions designed to interact with such files.
• Identify the variables you wish to convert by obtaining their variable IDs.
• Read the data from these variables into MATLAB's workspace.
• Convert the numeric data into strings. This could be done elementwise for vectors or cell-by-cell for matrices. MATLAB provides several functions for this purpose, such as “num2str”, “int2str”, or the string functions, depending on whether you want to create character arrays or string arrays.
• Ensure the conversion maintains the original data's precision and format, so the numerical values are accurately represented as strings.
• Close the “NetCDF” file once the operations are complete.

This process would transform the numeric data into a format suitable for text-based processing or display, while preserving the original values as accurately as possible in string form.

Below 2 scripts will give you a code overview of how you can create and save as well as modify the variable in any conversion type you want.

% Name of the sample NetCDF file
filename = 'sample.nc';

% Create the NetCDF file
ncid = netcdf.create(filename, 'CLOBBER');

% Define dimensions
dimid_x = netcdf.defDim(ncid, 'x', 10); % Dimension of length 10

% Define variables with different data types
varid_int16 = netcdf.defVar(ncid, 'var_int16', 'short', dimid_x);
varid_int32 = netcdf.defVar(ncid, 'var_int32', 'int', dimid_x);
varid_single = netcdf.defVar(ncid, 'var_single', 'float', dimid_x);

% End definitions and enter data mode
netcdf.endDef(ncid);

% Create sample data for each variable
data_int16 = int16(1:10);
data_int32 = int32(11:20);
data_single = single(21:30);

% Write sample data to the file
netcdf.putVar(ncid, varid_int16, data_int16);
netcdf.putVar(ncid, varid_int32, data_int32);
netcdf.putVar(ncid, varid_single, data_single);

% Close the NetCDF file
netcdf.close(ncid);

In above script variables are created and are stored for their type conversions to string in part 2.

% Re-open the NetCDF file for reading
ncid = netcdf.open(filename, 'NC_NOWRITE');

% Get variable IDs for the variables we created earlier
varid_int16 = netcdf.inqVarID(ncid, 'var_int16');
varid_int32 = netcdf.inqVarID(ncid, 'var_int32');
varid_single = netcdf.inqVarID(ncid, 'var_single');

% Read the data from the file
data_int16 = netcdf.getVar(ncid, varid_int16);
data_int32 = netcdf.getVar(ncid, varid_int32);
data_single = netcdf.getVar(ncid, varid_single);

% Convert the data to strings
str_int16 = string(data_int16);
str_int32 = string(data_int32);
str_single = string(data_single);

% Close the NetCDF file
netcdf.close(ncid);
disp(['String representation of int16 data: ' strjoin(str_int16, ', ')]);
disp(['String representation of int32 data: ' strjoin(str_int32, ', ')]);
disp(['String representation of single data: ' strjoin(str_single, ', ')]);

Here is the expected output.

"String representation of int16 data: "1, 2, 3, 4, 5, 6, 7, 8, 9, 10"

"String representation of int32 data: "11, 12, 13, 14, 15, 16, 17, 18, 19, 20"

"String representation of single data: "21, 22, 23, 24, 25, 26, 27, 28, 29, 30"

You can refer to following documents for more information regarding about how one can read data from variable in netCDF data source.

https://www.mathworks.com/help/matlab/ref/ncread.html

https://www.mathworks.com/help/matlab/ref/importdatatask.html

Hope this helps!