如何使用read.csv导入4位数字的年份值而不是2位数字

Question

I need to import dates using read.csv. The date are in "dd-mm-yyyy" format in csv file. I've appended sample data below.

UniqueId DOB

1. 01-04-1984
2. 24-08-1904
3. 12-12-2006
4. 05-05-1870

Read.csv is converting the date into "dd-mm-yy" format even when I'm importing date as character. I need it to import all 4-digit year.

My code and results are:

x <- read.csv("file", header=TRUE,colClasses =c("DOB"="character"))

I also tried:

x <- read.csv("file", header=TRUE, stringsAsFactors = FALSE)

Result from both:

UniqueId DOB

1. 01-04-84
2. 24-08-04
3. 12-12-06
4. 05-08-70

 > class(x$DOB) [1] "character" 

When I use as.Date function on this, I get error values:

> as.Date(dob$DOB, format="%d-%m-%y")  
[1] "01-04-1984" "24-08-2004" "12-12-2006" "05-08-1970"

I read that as.Date function automatically turns years between 00 and 68 into 21st Century years and years between 69 and 99 into 20th Century years.

Thus, I think I'm making a mistake in read.csv function itself.

Answer 1

I haven't figured out the way of achieving what you want in one line, but if you can afford splitting the task into two lines, then try this:

library(dplyr) # data frame operations
library(lubridate) # tidyverse-compliant package for operations on dates

x <- read.csv("file.csv", header=TRUE, stringsAsFactors=FALSE)
x <- x %>% mutate(DOB = as.Date(DOB, format="%d-%m-%Y"))
x %>% mutate(year = lubridate::year(DOB)) # just to verify that the operations on dates work as expected
#   UniqueID        DOB year
# 1        1 1984-04-01 1984
# 2        2 1904-08-24 1904
# 3        3 2006-12-12 2006
# 4        4 1870-05-05 1870