title: How to plot time Data
body: <p>My data structure looks like this:</p>
  
  <p><img src="https://i.stack.imgur.com/IcF7S.jpg" alt="Data"></p>
  
  <p>Now I want to select 3 cities and plot them over time (x=Date, y=Amount). Additionally, I want the months to be on the x-axis every 3 months. </p>
  
  <p>I tried ggplot, but it seems that my date is not defined correctly.</p>