My data is in a dataframe which has a structure like this:

```
df2 <- data.frame(Year = c("2007"), Week = c(1:12), Measurement = c(rnorm(12, mean = 4, sd = 1)))

```

Unfortunately I do not have the complete date (e.g. days are missing) for each measurement, only the Year and the Weeks (these are ISO weeks). 

Now I want to aggregate the Median of a Month's worth of measurements (e.g. the weekly measurements per month of the specific year) into a new column, Months. I did not find a convenient way to do this without having the exact day of the measurements available. Any inputs are much appreciated!