R: issue with line chart : I am having a problem to construct a line chart. Here is the output of my line chart. Why is the output like this, I mean the lines don`t touch (are not continuous). Maybe the issue is connected with my data format or type?[enter image description here][1] 

Thank you,
Hayk.
  [1]: https://i.stack.imgur.com/Yt7Ft.jpg