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Make third case parallel. 

Fixes #268
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hadley 2016-08-15 07:39:33 -05:00
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datetimes.Rmd
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@ -8,7 +8,7 @@ This chapter will show you how to work with dates and times in R. At first glanc
* Does every day have 24 hours?
* Does every minute have 60 seconds?
I'm sure you know that not every year has 365 days, but do you know the full rule for determining if a year is a leap year? (It has three parts.) You might have remembered that many parts of the world use daylight savings time (DST), so that some days have 23 hours, and others have 25. You probably didn't know that some minutes have 61 seconds because every now and then leap seconds are added because the Earth's rotation is gradually slowing down.
I'm sure you know that not every year has 365 days, but do you know the full rule for determining if a year is a leap year? (It has three parts.) You might have remembered that many parts of the world use daylight savings time (DST), so that some days have 23 hours, and others have 25. You might not have known that some minutes have 61 seconds because every now and then leap seconds are added because the Earth's rotation is gradually slowing down.
Dates and times are hard because they have to reconcile two physical phenomenon (the rotation of the Earth and its orbit around the sun) with a whole raft of geopolitical phenomenon including months, time zones, and DST. This chapter won't teach you every last detail about dates and times, but it will give you a solid grounding of practical skills that will help you with common data analysis challenges.