如何从Bokeh ColumnDatasource中提取数据

问题描述

我试图避免使用ColumnDataSource，而是将pandas dataframe列直接传递给Bokeh图.

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

尽管很快我必须实现一个HoverTool，它要求将数据存储在ColumnDataSource中.因此，我开始使用ColumnDataSource.

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

现在，我正在创建一个框注释，并且必须使用数据中某列的最大值来定义框的顶部边框.

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.

我可以使用熊猫轻松做到这一点:

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')

但是我不知道如何从ColumnDataSource中提取最大值.

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

是否有一种方法可以从中提取最大值，或者我的方法首先是错误的?

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

推荐答案

ColumnDataSource对象具有属性data，该属性将首先返回用于创建该对象的python字典.

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'] ))

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