title: Converting zoo time series from daily to monthly means
body: <p>I have created a time series using zoo. It has daily values for a long period of time (40 years). I can easily plot it, but what I want is to create a time series with monthly (mean) values from this original time series and then plot it as monthly values.</p>
  
  <p>I thought the package lubridate could be a good option for this and maybe there is an easy way but I don't see how. I'm a beginner in R. Has somebody a tip here?</p>