R Date and Time — Temporal Data Mastery

Learning Objectives

By the end of this tutorial, you will be able to:

• Create date and datetime objects in R
• Extract components (year, month, day, hour, minute)
• Perform date arithmetic and calculate differences
• Format dates for display and parsing
• Use the lubridate package for intuitive date operations

Date and Time Classes

# Current date and time
Sys.Date()        # [1] "2024-01-15"
Sys.time()        # [1] "2024-01-15 10:30:00 UTC"

Creating Dates

From Strings

# as.Date() — standard format (YYYY-MM-DD)
as.Date("2024-01-15")
# [1] "2024-01-15"

# Custom format
as.Date("15/01/2024", format = "%d/%m/%Y")
# [1] "2024-01-15"

as.Date("Jan 15, 2024", format = "%b %d, %Y")
# [1] "2024-01-15"

Common Format Codes

From Individual Components

# as.Date() with components
as.Date("2024", "01", "15")
# [1] "2024-01-15"

# From numeric (days since 1970-01-01)
as.Date(19736)
# [1] "2024-01-15"

Creating Datetimes

as.POSIXct()

# From string
as.POSIXct("2024-01-15 10:30:00")
# [1] "2024-01-15 10:30:00"

# With timezone
as.POSIXct("2024-01-15 10:30:00", tz = "US/Eastern")
# [1] "2024-01-15 10:30:00 EST"

# Custom format
as.POSIXct("15/01/2024 10:30", format = "%d/%m/%Y %H:%M")
# [1] "2024-01-15 10:30:00"

Sys.time() and Sys.time()

now <- Sys.time()
now
# [1] "2024-01-15 10:30:45 UTC"

class(now)   # [1] "POSIXct" "POSIXt"

Extracting Components

date <- as.POSIXct("2024-06-15 14:30:45")

# Extract components
format(date, "%Y")    # "2024"
format(date, "%m")    # "06"
format(date, "%d")    # "15"
format(date, "%H")    # "14"
format(date, "%M")    # "30"
format(date, "%S")    # "45"

# lubridate functions
library(lubridate)

year(date)     # [1] 2024
month(date)    # [1] 6
day(date)      # [1] 15
hour(date)     # [1] 14
minute(date)   # [1] 30
second(date)   # [1] 45

# Day of week
wday(date)             # 7 (Sunday)
wday(date, label = TRUE)  # Sun

# Day of year
yday(date)     # [1] 167

# Week
week(date)     # [1] 24

Date Arithmetic

# Add/subtract days
today <- as.Date("2024-01-15")
today + 7          # [1] "2024-01-22"
today - 3          # [1] "2024-01-12"

# Difference between dates
date1 <- as.Date("2024-01-15")
date2 <- as.Date("2024-06-15")
date2 - date1      # Time difference of 152 days
as.numeric(date2 - date1)  # [1] 152

# Datetime arithmetic
now <- Sys.time()
now + 3600         # +1 hour (in seconds)
now + 7*24*3600    # +1 week

lubridate Arithmetic

library(lubridate)

# Intuitive additions
now <- ymd_hms("2024-01-15 10:30:00")
now + days(7)
now + weeks(1)
now + months(3)
now + years(1)
now + hours(2) + minutes(30)

# Intervals
start <- ymd("2024-01-01")
end <- ymd("2024-12-31")
interval <- start %--% end
interval / days(1)  # 365 days

Formatting Dates

# format() — date to string
date <- as.Date("2024-01-15")
format(date, "%B %d, %Y")        # "January 15, 2024"
format(date, "%d/%m/%Y")          # "15/01/2024"
format(date, "%a, %b %d")         # "Mon, Jan 15"

# strftime — same as format
strftime(date, "%Y-%m-%d")

# paste for custom formats
paste(month(date, label = TRUE), day(date), year(date))
# [1] "Jan 15 2024"

Parsing with lubridate

library(lubridate)

# Flexible parsing functions
ymd("2024-01-15")           # [1] "2024-01-15"
mdy("01/15/2024")           # [1] "2024-01-15"
dmy("15/01/2024")           # [1] "2024-01-15"

# With time
ymd_hms("2024-01-15 10:30:00")
# [1] "2024-01-15 10:30:00 UTC"

# Partial parsing
ymd("2024-01")
# [1] "2024-01-01"

# Numeric input
ymd(20240115)
# [1] "2024-01-15"

Time Zones

library(lubridate)

# Current time in different zones
now <- now()
with_tz(now, "US/Eastern")
with_tz(now, "Europe/London")
with_tz(now, "Asia/Tokyo")

# Change timezone (doesn't change the time, just the label)
x <- ymd_hms("2024-01-15 10:30:00", tz = "UTC")
force_tz(x, tz = "US/Eastern")

Practical Examples

Example 1: Age Calculator

calculate_age <- function(birth_date) {
  today <- Sys.Date()
  age <- as.integer(format(today, "%Y")) - as.integer(format(birth_date, "%Y"))
  if (format(today, "%m%d") < format(birth_date, "%m%d")) {
    age <- age - 1
  }
  age
}

calculate_age(as.Date("1990-05-20"))

Example 2: Business Days

library(bizdays)

# Create calendar
cal <- create.calendar("Brazil/ANBIMA", holidays = holidaysANBIM)

# Business days between dates
bizdays(as.Date("2024-01-01"), as.Date("2024-12-31"), cal)

Example 3: Date Ranges

library(lubridate)

# Generate sequence of dates
seq(ymd("2024-01-01"), ymd("2024-01-10"), by = "day")
seq(ymd("2024-01-01"), ymd("2024-12-31"), by = "month")
seq(ymd("2024-01-01"), ymd("2024-12-31"), by = "quarter")

Practice Exercises

Exercise 1: Date Parser

Write a function that parses dates in multiple formats (YYYY-MM-DD, DD/MM/YYYY, MM-DD-YYYY).

Solution

library(lubridate)

parse_date <- function(date_str) {
  # Try different formats
  result <- tryCatch(
    ymd(date_str),
    error = function(e) tryCatch(
      mdy(date_str),
      error = function(e) tryCatch(
        dmy(date_str),
        error = function(e) NA
      )
    )
  )
  result
}

parse_date("2024-01-15")
parse_date("01/15/2024")
parse_date("15/01/2024")

Key Takeaways

• Use as.Date() for dates, as.POSIXct() for datetimes
• lubridate makes date operations intuitive — ymd(), mdy(), dmy()
• Format codes control parsing and display — %Y, %m, %d, %H, %M
• Date arithmetic works automatically — add/subtract days, months, years
• Sys.Date() and Sys.time() get current date/time
• wday(), yday(), week() extract temporal components
• Always specify timezones when working with datetimes

Next: Learn about R File Handling — reading and writing files.