How to divide a date column in two columns only-CodePudding

I have a data frame containing 1 date column:

> head(df$date)
[1] "1952-02-03" "1958-02-08" "1958-02-08" "1958-02-08" "1965-02-07" "1966-03-03"

The format is as you can see: "Y%-m%-d%"

I want to create two columns from this one, one containing the Years only and the second one containing the month and the day together.

Output wanted

year	month_day
1952	02-03
1958	02-08

and so on.

I tried this:

setDT(df)[, c("year", "month_day") := 
         c(tstrsplit(date, "-", type.convert = TRUE))]

but of course I get this error message: Supplied 2 columns to be assigned 3 items. which I fully understand but I cannot find anywhere the syntax to split only in two columns the date information.

Many thanks.

CodePudding user response：

Just use format to get the parts of the date you want:

df$year  <- format(df$date, "%Y")
df$month_day  <- format(df$date, "%m-%d")

df

#         date year month_day
# 1 1952-02-03 1952     02-03
# 2 1958-02-08 1958     02-08
# 3 1958-02-08 1958     02-08
# 4 1958-02-08 1958     02-08
# 5 1965-02-07 1965     02-07
# 6 1966-03-03 1966     03-03