Today, I came to know about the new thing. Whenever I wanted (or tried) to print math symbol (\leq, \sigma) through .CSV. It was giving an error. Because we can’t read LaTeX symbols directly from CSV. So, to read this, we will use \(math\) like this \(\leq\) in CSV to read any symbol.
Secondly, I did not know, how to define NULL values in the table using pgfplotstable? I was doing wrong. “I defined ‘nan’ for this, But it did not work”. If we want to define NULL values then leave it blank and separated by commas.