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

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!)

Take Hint (-30 XP)

Exercise

Subtraction of dates

Instructions