CODEWITHSUNDEEP
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Kristian Bjerke
Kristian Bjerke

Reputation: 27

Need help turning a column from character to date in R

Im trying to convert a column from character to date.

The current format in the column is "YearMmonth", as in "1990M01". It is a really weird format, so i'm wondering how R reads this when i use the as.Date code. It is basically "Year Month Month-number". I know how to use the rest of the code, i just need to know how to translate this to R.

I have tried using 

df <- as.Date(df, "%YM%m", "%Y/%m")

df <- as.Date(paste0("01-", df), format = "%Y/%m/%d")

and alot others, the main problem is translating the character column.

Upvotes: 0

Views: 178

Answers (1)

G. Grothendieck
G. Grothendieck

Reputation: 269371

There are several problems with the code in the question:

  • The first attempt in the question does not have a day field
  • the second attempt does but puts the day field first yet the format says it is last.
  • the use of df in the question suggests that the result is a data frame yet the result is a Date class object, not a data frame.

Here are some approaches that work.

yearmon

Use as.yearmon to convert to a yearmon object or as.Date(as.yearmon(...)) to convert to a Date object. yearmon objects directly represent year and month without day so that may be preferable.

library(zoo)

as.yearmon("1990M01", "%YM%m")
## [1] "Jan 1990"

as.Date(as.yearmon("1990M01", "%YM%m"))
## [1] "1990-01-01"

Replacing the M with a minus would also work:

as.yearmon(chartr("M", "-", "1990M01"))
## [1] "Jan 1990"

Base R

A way that does not involve any packages is to append a day:

as.Date(paste("1990M01", 1), "%YM%m %d")
## [1] "1990-01-01"

or change the M to a minus and append a minus and a 1 in which case it is already in the default format and no format string is needed.

as.Date(sub("M(\\d+)", "-\\1-1", "1990M01"))
## [1] "1990-01-01"

Upvotes: 2

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