How do I use "netcdf.getVar" to read a part of a variable?

I have an NC file with a large matrix in it. I would like to read only a portion of that matrix into memory for my calculation. How can I do this?

Answer 1

[MathWorks Support Team]

First, the best way to easily improve efficiency in NETCDF I/O operations is to use the low level library in MATLAB. You can find documentation on that here: 

https://www.mathworks.com/help/matlab/network-common-data-form.html

Essentially, the system works as described in the attached "exampleNETCDF.m" file. 

In order to read a portion of the variable, you need to

1. open the file

2. get the variable ID

3. use "netcdf.getVar" with the appropriate starting row/column and number of rows/columns

4. close the file

The syntax for "netcdf.getVar" is as such:

>> data = netcdf.getVar(ncid,varid,start,count)start = [startRow-1, startCol-1]

because MATLAB is 1-indexed and NETCDF is 0-indexed.

count = [numRows, numCols]