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Merge branch 'master' of github.com:hadley/r4ds 

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#	communicate.Rmd
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hadley 2016-08-25 16:45:01 -05:00
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communicate.Rmd
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# Introduction {#communicate-intro}
So far, you've learned the tools to get your data into R, tidy it into a form convenient for analysis, and then understand you data through transformation, visualisation and modelling. Next you'll learn how to __communicate__ your results because it doesn't matter how great your analysis is unless you can explain it to someone else.
So far, you've learned the tools to get your data into R, tidy it into a form convenient for analysis, and then understand your data through transformation, visualisation and modelling. However, it doesn't matter how great your analysis is unless you can explain it to others: you need to __communicate__ your results.
```{r echo = FALSE, out.width = "75%"}
knitr::include_graphics("diagrams/data-science-communicate.png")

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datetimes.Rmd
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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.
Dates and times are hard because they have to reconcile two physical phenomena (the rotation of the Earth and its orbit around the sun) with a whole raft of geopolitical phenomena 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.
### Prerequisites
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## Time spans
Next you'll learn about how arithmetic with dates works, including substraction, addition, and division. Along the way, you'll learn about three important classes that represent time spans:
Next you'll learn about how arithmetic with dates works, including subtraction, addition, and division. Along the way, you'll learn about three important classes that represent time spans:
* __durations__, which represent an exact number of seconds.
* __periods__, which represent human units like weeks and months.