Default null_value does not render correctly

[kwinkunks]

Thank you for this library; I'm using it in gio.

The default null value of 1e+30 is passed to a format string like "{0:>{1}.{2}f}".format(1e30, 12, 4) (see line in code) and produces '1000000000000000019884624838656.0000' instead of '1e+30 or possibly '1.0000e+30'.

Could fix by using the str() of the null value for NaNs, and the current format string for 'normal' values. Or you could change the format string to something like "{0:>{1}.{2}e}" (which would use scientific notation for everything, not sure if that's desirable).

I will submit a PR for a fix; you can decide what to do with it!

[baylejs]

Yes, been fighting this too. I changed the format string to general "{0:>{1}.{2}g}" and tested the import of the resulting file. Value by value basis would be best as you also suggest.

[baylejs]

I had to spend a little more time on this for reading zmap file into a legacy mapping application. Got it working nicely now.

In zmap.py use a string for null. null_value='0.1000000E+31',

In writer.py use conditional formatting depending on if the val is a number or a nan, which I set to -9999.999 temporarily for replacing with string null_value.

fmt = "{0:>{1}.{2}f}".format
width = zmap.field_width
precision = zmap.decimal_places
fmtNull = "{0:>{1}}".format
# zmap.z_values = np.nan_to_num(zmap.z_values, nan=zmap.null_value)
zmap.z_values = np.nan_to_num(zmap.z_values, nan=-9999.999)

def write_lines(r):
    # line_gen = ("".join(line) + "\n" for line in chunks([fmt(val, width, precision) for val in r], nodes_per_line))
    line_gen = ("".join(line) + "\n" for line in chunks([fmt(val, width, precision) if val != -9999.999 else fmtNull(zmap.null_value, width) for val in r], nodes_per_line))