How do I extract data from a Bokeh ColumnDatasource

Question

I was trying to avoid using a ColumnDataSource and instead of that I was passing pandas dataframe columns directly to Bokeh plots.

Soon though I had to implement a HoverTool which requires to have the data in a ColumnDataSource. So, I started using ColumnDataSource.

Now, I was creating a box annotation and I had to use the maximum value of a certain column from my data to define the top border of the box.

I can do that easily using pandas:

low_box = BoxAnnotation(
    top=flowers['petal_width'][flowers['species']=='setosa'].max(),
    fill_alpha=0.1, fill_color='red')

But I can't figure out how to extract the maximum from a ColumnDataSource.

Is there a way to extract a maximum value from it, or is my approach all wrong in the first place?

Solution 1

A ColumnDataSource object has an attribute data which will return the python dictionary used to create the object in the first place.

from bokeh.plotting import ColumnDataSource

# define ColumnDataSource
source = ColumnDataSource(
    data=dict(
        x=[1, 2, 3, 4, 5],
        y=[2, 5, 8, 2, 7],
        desc=['A', 'b', 'C', 'd', 'E'],
    )
)

# find max for variable 'x' from 'source'
print( max( source.data['x'] ))

Solution 2

If the source input is a Pandas DataFrame, you can use the Standard method:

source = ColumnDataSource(
    data= pd.DataFrame( dict(
        x=[1, 2, 3, 4, 5],
        y=[2, 5, 8, 2, 7],
        desc=['A', 'b', 'C', 'd', 'E'],
    ))
)
print( source.data['x'].max() )