It is rough. There are many ways that different tools put NAs, na, N/A, "", etc. in a file. To chose only "NA" would mean I would be excluding the output of other tools. I chose accessibility over specificity. #trade-offs.
Well, I think being promiscuous with "NA", "N/A", nan, etc. is a separate issue from a blank cell. A blank cell is literally missing. That should be filled with NA.
Fair enough but that doesn't explain why you chose to display all of them as "NA". As you say there are lots of different ones, hence it would be a bad idea to pick one as the 'default' to display. To me it's important whether something is missing, filled with "N/A", or "null", or "Not Applicable" etc.
Simple: provide CLI switches to let the user decide what they want for NA detection (current behavior as default, user can provide alternate NA values, per the source file or the natural language it is expressed in), and how they want them displayed, whether as-is, blank or a consistent custom value
(as-is should be the default).
