Parsing Dates in R: A Step-by-Step Guide

Introduction

As a data analyst or scientist, working with dates can be a challenging task. In this article, we will discuss how to parse dates from one format to another using the lubridate package in R. We will explore various methods and techniques to achieve this, including setting the locale.

Understanding the Problem

The problem at hand is to convert a string vector of dates in a specific format to a vector of dates in a different format. The input dates are in the format “%B %d, %Y”, while the desired output format is “%Y-%m-%d”. We have tried using the lubridate package’s mdy() function and as.Date() function, but both attempts resulted in a string of NA.

Setting the Locale

The issue lies in the locale settings. The lubridate package expects the names of months to be in Italian for the conversion to work correctly. However, the input dates are in English. To resolve this, we need to set the locale to match the input data.

Registering the Old Locale

Before setting a new locale, it is essential to register the old locale so that we can restore it later.

OL <- Sys.getlocale("LC_TIME")

This line retrieves the current locale setting for the time category ("LC_TIME").

Setting the New Locale

Next, we set the new locale to “C”, which does not use any language-specific formatting. We will use this locale to parse the input dates.

Sys.setlocale("LC_TIME","C")

This line sets the locale for the time category to English.

Parsing Dates

Now that the locale has been set, we can attempt to parse the input dates using the mdy() function from the lubridate package.

library(lubridate)
dates <- "March 21, 2016"
format(mdy(dates),"%Y-%m-%d")

This code defines a vector of dates in the format “%B %d, %Y”, converts each date to the desired format using mdy(), and then prints the result.

Restoring the Old Locale

After parsing the input dates, we should restore the original locale setting using the old locale identifier.

Sys.setlocale("LC_TIME", OL)

This line sets the locale back to its original value, ensuring that subsequent date conversions will use the correct language-specific formatting.

Additional Considerations

There are a few additional considerations when working with dates in R:

• Date Format: The lubridate package supports various date formats. Refer to the package documentation for more information.
• Time Zones: When working with dates, it is essential to consider time zones. The lubridate package uses a default time zone, but you can specify a different time zone using the tz argument.
• Date Range Validation: To ensure that your date data is valid, use the valid_date() function from the lubridate package.

Example Use Cases

Here are some additional example use cases to demonstrate how to parse dates in R:

Converting Dates from Various Formats

# Convert a string of dates in "yyyy-mm-dd" format to a vector of dates
dates <- c("2016-03-21", "2016-03-09")
library(lubridate)
parsed_dates <- mdy(dates)

# Print the parsed dates
print(parsed_dates)

Parsing Dates with Time Zones

# Parse a string of dates in "yyyy-mm-dd hh:mm:ss" format, assuming UTC time zone
dates <- c("2016-03-21 14:30:00", "2016-03-09 12:45:00")
library(lubridate)
parsed_dates <- mdy(dates, tz = "UTC")

# Print the parsed dates
print(parsed_dates)

Validating Date Range

# Define a range of dates and validate them using valid_date()
from <- as.Date("2016-01-01")
to <- as.Date("2016-12-31")
dates <- seq(from, to, by = "day")

valid_dates <- sapply(dates, function(x) lubridate::valid_date(x))

# Print the results
print(valid_dates)

By following these steps and examples, you can effectively parse dates in R using the lubridate package. Remember to set the locale correctly and consider time zones when working with date data.

Last modified on 2025-03-20