Parsing dates with lubridate

1. Parsing dates with lubridate

Welcome to Chapter 2. In this chapter you'll learn about using the lubridate package to parse and manipulate dates. To get started you'll learn about importing dates. We'll talk about two options in lubridate: a whole set of functions whose names correspond to different formats, and the more general purpose parse_date_time, a function where the format is specified as an argument.

2. ymd()

Let's consider a familiar date from the last chapter: the 27th of February 2013. In lubridate the function ymd will parse a date when it is formatted year first, then month, then day. So, if we happen to have the date formatted according to ISO 8601, ymd will parse it successfully. What's great about ymd is it handles dates that are in the right order, but may or may not be exactly ISO 8601. For example, it ignores any separators, so a date that uses dots instead of dashes parses successfully. And the units don't even need to be numeric. If the month uses the english abbreviation that works too!

3. Friends of ymd()

What's neat about lubridate is that there are a whole family of functions like ymd where the function name specifies the expected format of the date. There's dmy for day, month, year, mdy for dates in the common US form: month, day, year. And so on. There are also functions like this for datetimes too. The date part of the function name is followed by an underscore, and then hms, hm or s. So, dmy_hm will read a date with an accompanying time. Unlike some of R's built-in functions, if you don't specify a timezone, lubridate will assume UTC.

4. parse_date_time(x = _, order = _)

While the ymd family of functions handles most dates, you may still run into cases where you need to be more specific. The function parse_date_time in lubridate, also parses dates, but you specify the order in a separate argument. The order is a string that describes the order of the components in a date, for example here it's the string dmy. parse_date_time has a handy feature where if the dates you need to parse are in more than one format, you can pass in more than one order. Just pass in a vector of strings to order.

5. Formatting characters

You can find all the possible formating characters on the help page for parse_date_time. Some will seem familiar, lower case y, m and d correspond to year, month and day. An upper case Y is a year without a century. Upper case H, M and S are hours, minutes and seconds. There are a few others that are useful: a specifies a weekday either abbreviated or in full, depending on the case, similarly b specifies a month name. Upper case I can parse 12 hour times and is often used with lower case p an AM/PM indicator. z parses timezones provided as offsets in hours and minutes from UTC.

6. Let's practice!

Now it's your turn, take what you've learned to parse some dates and times.

This exercise is part of the course

Working with Dates and Times in R

IntermediateSkill Level

5.0+

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R doesn't know something is a date or time unless you tell it. In this chapter you'll learn about some of the ways R stores dates and times by exploring how often R versions are released, and how quickly people download them. You'll also get a sneak peek at what you'll learn in the following chapters.

Exercise 1: Introduction to dates Exercise 2: Recognizing ISO 8601 dates Exercise 3: Specifying dates Exercise 4: Automatic import Exercise 5: Why use dates?Exercise 6: Plotting Exercise 7: Arithmetic and logical operators Exercise 8: What about times?Exercise 9: Getting datetimes into R Exercise 10: Datetimes behave nicely too Exercise 11: Why lubridate?

Dates and times come in a huge assortment of formats, so your first hurdle is often to parse the format you have into an R datetime. This chapter teaches you to import dates and times with the lubridate package. You'll also learn how to extract parts of a datetime. You'll practice by exploring the weather in R's birthplace, Auckland NZ.

Exercise 1: Parsing dates with lubridate

Current Exercise

Exercise 2: Selecting the right parsing function Exercise 3: Specifying an order with `parse_date_time()`Exercise 4: Weather in Auckland Exercise 5: Import daily weather data Exercise 6: Import hourly weather data Exercise 7: Extracting parts of a datetime Exercise 8: What can you extract?Exercise 9: Adding useful labels Exercise 10: Extracting for plotting Exercise 11: Extracting for filtering and summarizing Exercise 12: Rounding datetimes Exercise 13: Practice rounding Exercise 14: Rounding with the weather data

Getting datetimes into R is just the first step. Now that you know how to parse datetimes, you need to learn how to do calculations with them. In this chapter, you'll learn the different ways of representing spans of time with lubridate and how to leverage them to do arithmetic on datetimes. By the end of the chapter, you'll have calculated how long it's been since the first man stepped on the moon, generated sequences of dates to help schedule reminders, calculated when an eclipse occurs, and explored the reigns of monarch's of England (and which ones might have seen Halley's comet!).

Exercise 1: Taking differences of datetimes Exercise 2: How long has it been?Exercise 3: How many seconds are in a day?Exercise 4: Time spans.Exercise 5: Adding or subtracting a time span to a datetime Exercise 6: Duration or Period?Exercise 7: Arithmetic with timespans Exercise 8: Generating sequences of datetimes Exercise 9: The tricky thing about months Exercise 10: Intervals Exercise 11: Examining intervals. Reigns of kings and queens Exercise 12: Comparing intervals and datetimes Exercise 13: Converting to durations and periods

You now know most of what you need to tackle data that includes dates and times, but there are a few other problems you might encounter in practice. In this final chapter you'll learn a little more about these problems by returning to some of the earlier data examples and learning how to handle time zones, deal with times when you don't care about dates, parse dates quickly, and output dates and times.

Exercise 1: Time zones Exercise 2: Setting the timezone Exercise 3: Viewing in a timezone Exercise 4: Timezones in the weather data Exercise 5: Times without dates Exercise 6: More on importing and exporting datetimes Exercise 7: Fast parsing with fasttime Exercise 8: Fast parsing with lubridate::fast_strptime Exercise 9: Outputting pretty dates and times Exercise 10: Wrap-up