What is the source of the index in a ColumnDataSource created from a pandas DataFrame?

Question

Dataframes naturally come with an index, i.e. those set of row headers we can think of them as. When I construct a ColumnDataSource in bokeh to capture the information in that dataframe for plotting and annotating in a HoverTool I see that the hover tool has a built in ( "index" , "$index" ) tooltip available. Will this index be identical to my dataframe's index or is it simply the row index in the ColumnDataSource

Answer 1

The special variable $index simply displays the row index of the column data source (it can't be a pandas index in general, because although CDS may be created from data frames, they do not have to). If you want to include the pandas dataframe index you can add it:

In [5]: d = pd.DataFrame(dict(a=[1,2,3], b=[2,3,4]))

In [6]: d.index
Out[6]: RangeIndex(start=0, stop=3, step=1)

In [7]: source = ColumnDataSource(d)

In [8]: source.add(d.index, 'index')

This field can be accessed in a hover tool with the standard and general @colname syntax for any standard CDS column (so in this specific case: @index)