R as.Date() Function: Working with Dates

The as.Date() function in R converts various types of date and time objects or character strings into Date objects.

Syntax

as.Date(x, 
        format, 
        tryFormats = c("%Y-%m-%d", "%Y/%m/%d"),
        optional = FALSE, tz = "UTC",
        origin,
        ...)

Parameters

Name	Description
x	It is an object to be converted.
format	It is a character string. If the format argument is not specified, it will tryFormats one by one on the first non-NA element and give an error if none works. Otherwise, the processing is via strptime.
tryFormats	It is a character vector of format strings to try if the format is not specified.
optional	It is a logical argument to return NA (instead of signaling an error) if the format guessing fails.
origin	It is a Date object or something that can be coerced.Date(origin, …) to such an object.
tz	It is a time zone name.

Basic usage

dates <- c("20nov1980", "20nov1991", "20nov1993", "10sep1993")

dt <- as.Date(dates, "%d%b%Y")

dt

# Output: [1] "1980-11-20" "1991-11-20" "1993-11-20" "1993-09-10"

Converting numeric values to dates

Numeric values can also be converted to dates. By default, numeric conversion assumes the number represents the number of days since 1970-01-01 (the Unix epoch):

# Numeric representation of a date (days since 1970-01-01)
date_numeric <- 19320

# Convert to Date
date_object <- as.Date(date_numeric, origin = "1970-01-01")

# Print the result
print(date_object)

# Output: [1]  "2022-11-24"

Unrecognizable Date Formats

In the above figure, we took a vector of unrecognizable date formats and converted it into a vector of proper dates.

dates <- c("11/20/80", "11/20/91", "11/20/1993", "09/10/93")

dt <- as.Date(dates, "%m/%d/%y")

dt

# Output: [1] "1980-11-20" "1991-11-20" "2019-11-20" "1993-09-10"

Setting timezone

To set the timezone, use the tz argument.

If your computer system’s time is set to PST8PDT, you can use the tz=” “ argument, which means “use the current system time zone”.

In the above figure, we passed the timezone explicitly using the “tz” argument that the output is a proper date.

as.Date("2022/05/27 12:30", tz = "PST8PDT")

# Output: [1] "2022-05-27"

Returning NA argument

The as.date() function returns NA if the locale has not been set properly according to your system.

The above figure illustrates that if you don’t set the locale properly according to your system, it will return the “NA” value.

factr <- as.factor("27/05/2022")
date <- as.Date(factr, format = "%Y-%m-%d")

print(factr)
print(date)

# Output:
# [1] 27/05/2022
# Levels: 27/05/2022

# [1] NA

To handle NA values, convert the factor into POSIXt and a date.

a <- as.factor("27/05/2022")
pos_dt <- strptime(a, format = "%d/%m/%Y")
b <- as.Date(pos_dt, format = "%Y-%m-%d")

print(a)
print(b)

# Output:
# [1] 27/05/2022
# Levels: 27/05/2022
# [1] "2022-05-27"

That’s it.

Krunal Lathiya

Krunal Lathiya is a seasoned Computer Science expert with over eight years in the tech industry. He boasts deep knowledge in Data Science and Machine Learning. Versed in Python, JavaScript, PHP, R, and Golang. Skilled in frameworks like Angular and React and platforms such as Node.js. His expertise spans both front-end and back-end development. His proficiency in the Python language stands as a testament to his versatility and commitment to the craft.