title: R - geom_line() transforming points to vertical lines
body: <p>I am melting a data frame in order to plot it in ggplot2. However,
  <code>geom_line()</code> is not giving me horizontal lines. Instead it is transforming my points to vertical lines. I will attach images and add the code to further illustrate:</p>
  
  <p>Using only <code>geom_point()</code>:</p>
  
  <pre><code>vecmmelt = melt(tail(tempdf,7), id.vars = "Date")
  
  ggplot(vecmmelt, aes(x = Date, y = value, colour = variable, group=1)) +geom_point()+theme_bw()
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/NhNnR.png" alt="Using geom point only"></p>
  
  <p>Now I would expect to have the following when using <code>geom_line()</code>:</p>
  
  <p><img src="https://i.stack.imgur.com/WS0pJ.png" alt="Expectation from + geom_line"></p>
  
  <p>What I am really getting by using the following code is the following picture:</p>
  
  <pre><code>vecmmelt = melt(tail(tempdf,7), id.vars = "Date")
  
  ggplot(vecmmelt, aes(x = Date, y = value, colour = variable, group=1)) +geom_point()+geom_line()
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/h5j8i.png" alt="Reality that is wrong"></p>
  
  <p>I tried using <code>geom_path()</code> and it also is wrong</p>