如何在R语言中将字符串转换为日期？含特定格式转换问询

Great questions! Let's break this down step by step to solve your R date conversion needs.

Converting strings to date objects in R is a common task, and you have two reliable approaches: using base R functions, or leveraging the flexible lubridate package (my go-to for date handling).

Base R: as.Date() #

The core as.Date() function works when you specify the format of your string using these common format codes:

• %Y: 4-digit year (e.g., 2020)
• %m: 2-digit month (01-12)
• %d: 2-digit day (01-31)
• %b: Abbreviated month name (Jan, Feb)
• %B: Full month name (January, February)

Examples of how to use it:

# Standard "YYYY-MM-DD" format (no need to specify format)
date_str1 <- "2020-01-19"
as.Date(date_str1)

# "DD/MM/YYYY" format (requires explicit format)
date_str2 <- "19/01/2020"
as.Date(date_str2, format = "%d/%m/%Y")

# String with full month name
date_str3 <- "January 19, 2020"
as.Date(date_str3, format = "%B %d, %Y")

lubridate Package (Simpler & More Flexible) #

lubridate takes the guesswork out of date formats—you just need to match the order of day/month/year in your string with the corresponding function:
First install and load the package:

install.packages("lubridate")
library(lubridate)

Then use these intuitive functions:

# For "YYYY-MM-DD"
ymd("2020-01-19")

# For "DD/MM/YYYY"
dmy("19/01/2020")

# For "Month Day, Year"
mdy("January 19, 2020")

The catch here is the ordinal suffix (th) attached to the day. Base R's as.Date() can't parse this directly, but we have two easy workarounds:

Method 1: Clean the String First #

Use regex to strip off ordinal suffixes (st, nd, rd, th) before converting. You can use base R or the stringr package for this:

# Load stringr (install first if needed: install.packages("stringr"))
library(stringr)

date_str <- "19th January 2020"
# Remove ordinal suffixes with regex
clean_date <- str_replace(date_str, "(\\d+)(st|nd|rd|th)", "\\1")
# Now convert the cleaned string
as.Date(clean_date, format = "%d %B %Y")

Method 2: Let lubridate Handle It #

lubridate's functions are smart enough to ignore ordinal suffixes automatically:

library(lubridate)
date_str <- "19th January 2020"
# dmy() matches day-month-year order and skips the "th"
dmy(date_str)

This will directly return a standard R Date object: [1] "2020-01-19"

内容的提问来源于stack exchange，提问作者Bogaso