Extract Month from Week and Year number [duplicate

Question

This question already has answers here:

Transform year/week to date object (2 answers)

Get the month from the week of the year (3 answers)

Closed 2 years ago.

I have a dataframe where I extracted the week and year number using lubridate. I do not have the date values anymore.

I want to extract the month from the week number and year number.

df
Week    Year  
   1    2018
   5    2018
  45    2017

I want my final output to be this:

Week    Year  Month
   1    2018      1
   5    2018      2
  45    2017     11

Answer 1

This extracts the month of the first day of the week, you could add a constant or something if you wanted the 2nd or 3rd day of the week instead.

df %>% 
  mutate(Month = month(ymd(Year * 10000 + 0101) + Week * 7))