title: How to display custom index using Bokeh hover tool?
body: <p>I'm using Bokeh to plot the results of ~700 simulations against another set of results using a scatter plot. I'd like to use the hover tool to qualitatively determine patterns in the data by assigning a custom index that identifies the simulation parameters. </p>
  
  <p>In the code below, <code>x</code> and <code>y</code> are the columns from a Pandas DataFrame which has the simulation IDs for the index. I've been able to assign this index to an array using <code>&lt;DataFrameName&gt;.index.values</code> but I haven't found any documentation on how to assign an index to the hover tool. </p>
  
  <pre><code># Bokeh Plotting
  h = 500
  w = 500
  default_tools = "pan, box_zoom, resize, wheel_zoom, save, reset"
  custom_tools = ", hover"
  fig = bp.figure(x_range=xr, y_range=yr, plot_width=w, plot_height=h, tools=default_tools+custom_tools)
  fig.x(x, y, size=5, color="red", alpha=1)
  bp.show(fig)
  </code></pre>