title: How to plot multiple curves and color them as group using R ggplot
body: <p>I have a data frame like this.</p>
  
  <pre><code>      ID     read1     read2     read3     read4 class
  1     5820350 0.3791915 0.3747022 0.3729779 0.3724259     1
  2     5820364 0.3758676 0.3711775 0.3695976 0.3693112     2
  3     5820378 0.3885081 0.3823900 0.3804273 0.3797707     2
  4     5820392 0.3779945 0.3729582 0.3714910 0.3709072     1
  5     5820425 0.2954782 0.2971604 0.2973882 0.2973216     3
  6     5820426 0.3376101 0.3368173 0.3360203 0.3359517     3
  </code></pre>
  
  <p>Each row represents one sample with four values,and the last column is the classification of this sample. I want to visualize each sample curve and set the class as the color. 
  I tried to reshape the data frame, but I then lost the class feature which I need. 
  Could you please give me some hint or show me how to do that in R?</p>
  
  <p>Thanks in advance.</p>