title: Changing week+day(39+3) variable into either week or days in R
body: <p>Im working with a pregnancy-lenght [factor] variable that is given in number of weeks+days(39+3) and I need to be able to work with a whole number that i can compare between groups and calculate the mean. So either 276 days (37*7+3) or 37,43 weeks (37+(3/7)). 
  Any suggestion?</p>