Date & Time in R

In this lesson, you will learn how R works with dates and time values.

Date and time data is extremely common in real-world datasets such as logs, transactions, events, timestamps, and time-series records. Understanding how to handle them correctly is essential for analysis.

Why Date & Time Handling Is Important

Date and time values allow you to:

• Track trends over time
• Calculate durations and differences
• Group and summarize data by time periods
• Build time-based reports and dashboards

Date and Time Classes in R

R has built-in classes to represent date and time values.

The most common ones are:

• Date – stores calendar dates
• POSIXct – stores date and time as a timestamp
• POSIXlt – stores date and time as a list structure

Working with Dates Using as.Date()

The as.Date() function converts character strings into Date objects.

Dates must follow a recognizable format such as YYYY-MM-DD.

date1 <- as.Date("2025-01-15")
date1

Getting the Current Date

You can retrieve today’s date using the Sys.Date() function.

today <- Sys.Date()
today

Working with Date & Time Using Sys.time()

The Sys.time() function returns the current date and time.

It uses the POSIXct format, which is suitable for precise timestamps.

current_time <- Sys.time()
current_time

Extracting Date Components

You can extract parts of a date such as year, month, and day.

This is useful for grouping or filtering data.

date <- as.Date("2024-12-20")

year <- format(date, "%Y")
month <- format(date, "%m")
day <- format(date, "%d")

year
month
day

Calculating Differences Between Dates

R allows you to subtract dates to calculate durations.

The result is returned as a time difference object.

start_date <- as.Date("2024-01-01")
end_date <- as.Date("2024-01-10")

difference <- end_date - start_date
difference

Adding or Subtracting Days

You can easily add or subtract days from a date.

This is helpful when calculating deadlines or future dates.

future_date <- Sys.Date() + 7
past_date <- Sys.Date() - 30

future_date
past_date

Formatting Dates for Display

Dates can be formatted to improve readability.

This is especially important for reports and dashboards.

formatted_date <- format(Sys.Date(), "%d %B %Y")
formatted_date

Common Date & Time Mistakes

• Using incorrect date formats
• Mixing character strings and Date objects
• Ignoring time zones
• Not converting data types properly

📝 Practice Exercises

Exercise 1

Convert the string "2023-08-25" into a Date object.

Exercise 2

Find the number of days between two dates.

Exercise 3

Extract the year from today’s date.

Exercise 4

Add 15 days to the current date.

✅ Practice Answers

Answer 1

as.Date("2023-08-25")

Answer 2

as.Date("2024-01-15") - as.Date("2024-01-01")

Answer 3

format(Sys.Date(), "%Y")

Answer 4

Sys.Date() + 15

What’s Next?

In the next lesson, you will learn about Data Aggregation in R.

This will help you summarize and analyze data efficiently.