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Exercise

Subtraction of dates

Just like with numerics, arithmetic can be done on dates. In particular, you can find the difference between two dates, in days, by using subtraction:

today <- as.Date("2017-01-02")
tomorrow <- as.Date("2017-01-03")
one_year_away <- as.Date("2018-01-02")

tomorrow - today
Time difference of 1 days

one_year_away - today
Time difference of 365 days

Equivalently, you could use the difftime() function to find the time interval instead.

difftime(tomorrow, today)
Time difference of 1 days

# With some extra options!
difftime(tomorrow, today, units = "secs")
Time difference of 86400 secs
Instructions
100 XP
  • A vector of dates has been created for you.
  • You can use subtraction to confirm that January 1, 1970 is the first date that R counts from. First, create a variable called origin containing "1970-01-01" as a date.
  • Now, use as.numeric() on dates to see how many days from January 1, 1970 it has been.
  • Finally, subtract origin from dates to confirm the results! (Notice how recycling is used here!)
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