title: Plot multiple lines with holoviews
body: <p>I have a df that looks like this:</p>
  <pre><code>data = {'Cumulative': {0: 4, 1: 18, 2: 24, 3: 24, 4: 4, 5: 20, 6: 32, 7: 42},  'Id': {0: 1, 1: 1, 2: 1, 3: 1, 4: 2, 5: 2, 6: 2, 7: 2},  'Order': {0: '1-1',   1: '1-2',   2: '1-3',   3: '1-4',   4: '1-1',   5: '1-2',   6: '1-3',   7: '1-4'},  'Period': {0: 1, 1: 2, 2: 3, 3: 4, 4: 1, 5: 2, 6: 3, 7: 4},  'Time': {0: '1-1',   1: '1-2',   2: '1-3',   3: '1-4',   4: '1-1',   5: '1-2',   6: '1-3',   7: '1-4'},  'Year': {0: 1, 1: 1, 2: 1, 3: 1, 4: 1, 5: 1, 6: 1, 7: 1}}
  
  df = pd.DataFrame(data)
  </code></pre>
  <p>The resulting dataframe is as follows:</p>
  <p><a href="https://i.stack.imgur.com/j8AAI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/j8AAI.png" alt="example dataframe" /></a></p>
  <p>What I would like to do with Holoviews is plot a line for every id. So 'Order' is on the x-axis, 'Cumulative' on the y-axis and every 'Id' has it's own line (all with the same color). This is what I have so far, but it doesn't give me the right result.</p>
  <pre><code>%opts Curve [width=600 height=400 show_grid=True ] (color='indianred', alpha=0.5, line_width=1)
  
  kdims=['Order' ] vdims = ['Cumulative',
              ] ds = hv.Dataset(df.sort_values(by=['Year','Period']), kdims=kdims, vdims= vdims)
  
  ds.to(hv.Curve, ['Order'] ,'Cumulative' )
  </code></pre>