Thanks a lot for reporting this.

I was able to reproduce the problem with this manually created table of 10e5 columns:

echo 1 100000 | awk '{for(i=0;i<$2;++i) printf "%d ", $1+i; print ""}' > many-columns.txt

asttable many-columns.txt -i

Increasing the column count to 1e6 did indeed take very long and forced me to manually close it too.

The problem with plain-text tables is that the reading can't be easily parallelized (with FITS tables, since we know the number a-priori, in Gnuastro, we parallelize the column reading).

If you do come up with a good solution for plain-text tables in NEMO, please share it here.

In Gnuastro, we do have a format to give metadata to plain-text tables. But that also won't necessarily help unless all columns are string (their number of characters are known a-priori).

Generally, besides theoretical checking of code, I am curious if there is any real-world scenario that would require so many columns? Usually the workflow can be re-designed (optimized) to avoid so many columns in one file. For example FITS only accepts 999 columns.