Pretty date breaks

[hadley]

Need method like pretty() from base R that given a date range, provides a set of pretty breaks that nicely span the range.

[hadley]

See ggplot2::time_breaks and ggplot2::date_breaks for a place to start.

[garrettgman]

could you give me a better understanding of what pretty dates should accomplish? ggplot2::date_breaks returns an output that seems tailored for another function to use. (It doesn't seem that understandable on its own). What overall process is pretty dates a step in? Binning histograms? Also, what determines whether a date break is pretty (i.e, a certain number of them, breaks falling on round "numbers/dates", etc)?

[garrettgman]

I made a pretty.dates() with the following features:

1. identifies the unit each interval should be in to provide ~ n bins
2. chooses a "pretty" length for the intervals depending on their units
   An interval is "pretty" if its length is a factor of the next largest unit.
   pretty intervals of seconds are 1,2,5,10,15,30 and 60 seconds
   pretty intervals of minutes are 1,2,5,10,15,30 and 60 minutes
   pretty intervals of hours are 1,2,3,4,6,8,12, and 24 hours
   pretty intervals of months are 1,2,3,4,6, and 12 months
   years and days adopt the base::pretty numbering system - 1,2, or 5 times a power of 10
   weeks are always ugly, and hence not included
3. chooses the closest start and end points that are a) outside the range of data, and b) begin a series whose points will overlap with the start of the next complete hour, month, year (i.e. whatever the next largest unit is).

[hadley]

Sounds perfect!