[R] Converting "day of year" to "year", "month" and "day"

[Jibrin Alhassan]

Dear R users,
I am very new to R software. I have solar wind speed data needed for my
work. How do I convert day in the year to year, month, and day with R
software? I have used this code
as.Date(0, origin = "1998-01-01")
but it can only convert one day of the year at a time. Meanwhile, I have up
to the 1998-2002 data set. Attached is my data.
Kindly help, please.
Jibrin Alhassan