如何更改 R 中的日期样式？

Question

A column in my dataset includes dates such as Month Name and Year. I want to change the month's name to number.

My dataset looks like this (but is not limited to only 3 rows):

I want to change the ldr_start column to this: ldr_start 3/92 7/93 8/93

Thank you.

Answer 1

It's not really a "date" in either case. The zoo package does define a yearmon class. Here we can just use strsplit and process the month-character, match against the R Constant, month.abb , and then rejoin:

dat <- scan(text="Mar-92,Feb-93,Jul-94,Sep-95", what = "", sep=",")
#Read 4 items
datspl <- strsplit(dat, split="-")
sapply( datspl, function(mnyr){ paste( match(mnyr[1], month.abb), mnyr[2], sep="/")})
#[1] "3/92" "2/93" "7/94" "9/95"

Answer 2

We could also use stringr 's str_replace_all :

data <- c("Mar-92", "Jul-93", "Aug-93")

str_replace_all(data, setNames(as.character(1:12), month.abb))

Output:

[1] "3-92" "7-93" "8-93"

Answer 3

Using the input defined reproducibly in the Note at the end we have some alternatives.

1) yearmmon Using the test data in the Note at the end convert the input column to yearmon class and then format it in the desired fashion. See?strptime for information on the percent codes.

library(zoo)

transform(DF, start2 = sub("^0", "", format(as.yearmon(start, "%b-%y"), "%m/%y")))
##    start start2
## 1 Mar-92   3/92

1a) If it is ok to have a leading zero on one digit months then we can omit the sub and just write:

transform(DF, start2 = format(as.yearmon(start, "%b-%y"), "%m/%y"))
##    start start2
## 1 Mar-92  03/92

2) Base R Using only base R we can append 1 to start to make it a valid date (valid dates require year, month and day and not just month and year) and then proceed in a similar way as in (1) or (1a).

transform(DF, 
  start2 = sub("^0", "", format(as.Date(paste(start, 1),  "%b-%y %d"), "%m/%y")))
##    start start2
## 1 Mar-92   3/92

Note

DF <- data.frame(start = "Mar-92") # test data frame