title: ggplot Multi line plot from same dataframe
body: <p>I have this dataframe (df) :</p>
  
  <pre><code>  day     time      value
  20011101    93000 1.00000000
  20011102    93000 1.00000000
  20011105    93000 1.00000000
  20011101   100000 0.81958763
  20011102   100000 0.95412844
  20011105   100000 0.27610209
  20011101   103000 0.27835052
  20011102   103000 0.32415902
  20011105   103000 0.77958237
  20011101   110000 0.23711340
  </code></pre>
  
  <p>Sample here: <a href="https://www.dropbox.com/s/y7mtcay6ke9ydnm/sample.txt" rel="noreferrer">https://www.dropbox.com/s/y7mtcay6ke9ydnm/sample.txt</a></p>
  
  <p>Using ggplot, I'm trying to get a line for every single day where axis x = time, so in R I wrote:</p>
  
  <pre><code>ggplot(df, aes(x=time, y=value, colour=day)) + geom_line()
  </code></pre>
  
  <p>Unfortunately, this is what I got. I did not expect a plot like this.
  <img src="https://i.stack.imgur.com/1F4SV.jpg" alt="Graph from R"></p>
  
  <p>And this is an Excel graph. This is the one I'm looking for. A different line for every single day:</p>
  
  <p><img src="https://i.stack.imgur.com/WRw02.png" alt="enter image description here"></p>
  
  <p>I do not know how to tell R to join dots from same day...
  What's wrong? What am I missing?</p>
  
  <p>One more thing: As I have data from more than 5 years, I would prefer a one-color plot.</p>
  
  <p>Thanks for your help!</p>