FMT: allow datetime/timedelta formatting on a column to be better

[jreback]

http://stackoverflow.com/questions/16103238/pandas-timedelta-in-days/16104567#16104567

Its easy to think about, e.g. if no dates in a particular column have time values, then can print them w/o the time values (e.g. just 2001-01-01 maybe), I think this would be nice as the default (maybe add an option for it?)

In [17]: df
Out[17]: 
                  age               today                diff      years
0 2001-01-01 00:00:00 2013-04-19 00:00:00 4491 days, 00:00:00  12.304110
1 2004-06-01 00:00:00 2013-04-19 00:00:00 3244 days, 00:00:00   8.887671

Better?

In [17]: df
Out[17]: 
         age      today      diff     years
0 2001-01-01 2013-04-19 4491 days 12.304110
1 2004-06-01 2013-04-19 3244 days  8.887671

[cancan101]

Any reason that Timedelta64Formatter subclasses Datetime64Formatter rather than directly subclassing GenericArrayFormatter?

[jtratner]

@cancan101 It doesn't matter to preserve that hierarchy. Heck most of those formatters could be collapsed into one just by setting a _default_formatter property.

[cancan101]

Also for repr_timedelta64, would there be objections to change this method to not output the hms section of a timedelta if they are all zero?

In other words, rather than: 36 days, 00:00:00, just 36 days.

It would be a relatively simple change:

if days:
    return "%s%d days, %02d:%02d:%s" % (sign_pretty, days, hours, minutes,
                                           seconds_pretty)

to something like:

   if days:
       if hours or minutes or frac:
          return "%s%d days, %02d:%02d:%s" % (sign_pretty, days, hours, minutes,
                                           seconds_pretty)
      else:
          return "%s%d days" % (sign_pretty, days)

[jreback]

I think the change to repr_timedelta should involve a keyword arg . for the most part u DO want a full repr I think (eg in csv and such)

but for output formatting to say the console you could collapse it so need both modes

[jtratner]

My two cents: I like it for your age and today examples above with dates, but don't like it at all for timedeltas. Feels like it obscures the data that you actually have in the column.

[cancan101]

@jreback The full repr argument is a bit weak since even now it does not show the day section of the string when the number of days is 0.

[cancan101]

@jtratner I agree that for timedeltas it obscures the output of the data.

[jreback]

open to various display options

[jtratner]

I think this would be good:

In [17]: df
Out[17]: 
         age      today      diff          years
0 2001-01-01 2013-04-19 4491 days, 0:00:00 12.304110
1 2004-06-01 2013-04-19 3244 days, 0:00:00  8.887671

[jtratner]

and it has the benefit of being round-trippable

[jreback]

@jtratner iirc the short formats are round trip able as well

[jtratner]

'3244 days'? nice

[jreback]

yep I needed it for storing timedelta in hdf store actually
when u query (to make the query easy)

to_timedelta is pretty well tested for this

[jtratner]

well, if that's the case, I guess I'm fine either way.