Altair：创建组合的整体工具提示

如何解决Altair：创建组合的整体工具提示

我有一个斜率图，其中我标记了前后条件的值（使用 mark_point 和 mark_line，x 轴类型是名义上的）。我还使用 mark_rect 为背景着色（在计算变换中使用图表的宽度/高度）。

现在我想为矩形创建一个整体工具提示（而不是使悬停在斜坡的两个点上）。如何将斜率值汇总到一个工具提示位置（前值、后值）？

我已经开始尝试使用枢轴变换，但它不知道如何将每个图表的参数 (date_time) 的 post 和 pre 值合并到一个工具提示中

示例代码：

import pandas as pd
import altair as alt
from datetime import datetime
#https://vega.github.io/vega/docs/schemes/#redyellowgreen

data = pd.DataFrame({'value_rel': [0.41,0.52,0.39,0.58],'section': ['SECTION','SECTION','SECTION'],'parameter': ['ParaM1','ParaM1','ParaM1'],'date_time': [datetime(2018,4,19),datetime(2019,16),datetime(2018,16)],'value_class': ['medium','medium','heavy','medium'],'dilation': ['PRE','PRE','POST','POST'],'predicted': [3.06,3.04,3.06,3.04],'value': [1.25,1.68,1.21,1.74],'predicted_rel': [1,1,1],'title_de': ['ParaM_1','ParaM_1','ParaM_1'],'title_description_de': ['Parameter 1 %','Parameter 1 %','Parameter 1 %'],'diffs_rel': [None,None,-0.019,0.028],})

pd.set_option('display.max_rows',None)
pd.set_option('display.max_columns',None)
pd.set_option('display.width',None)
pd.set_option('display.max_colwidth',None)

# print(data)

parameter_encode_y = 'value_rel:Q'
slope_chart_width = 180
slope_chart_height = 180

min_y = data['value_rel'].min() * 0.9
max_y = data['value_rel'].max() * 1.1
custom_scale = alt.Scale(domain=[min_y,max_y])

slope_base = alt.Chart(data).encode(
    x=alt.X(
        'dilation',type='nominal',sort='descending',title=None,axis=None
    ),y=alt.Y(
        parameter_encode_y,axis=None,scale=custom_scale
    )
).properties(
    width=slope_chart_width,height=slope_chart_height
)


slope_points = slope_base.mark_point(
    filled=True,size=150,opacity=1,strokeWidth=1,stroke='black',clip=True
).encode(
    color=alt.Color(
        'value_class',title='severity'
        ),tooltip=[alt.Tooltip('value_class',title='Severity '),alt.Tooltip('dilation',title='Pre/Post Param'),alt.Tooltip('value',format='.3',title='Absolute'),alt.Tooltip('predicted',title='Target'),alt.Tooltip('value_rel',format='.1%',title='% of Target'),alt.Tooltip('diffs_rel',title='Change Pre-Post')
      ],strokeDash=alt.condition(
        alt.datum.dilation == 'PRE',alt.value([4,2]),alt.value([])
    )
)


slope_line = slope_base.mark_line(
    color='black',strokeWidth=1
)


slope_ruler = slope_base.mark_rule(
    color="#A6D96A",size=1,clip=True
).encode(
    x=alt.X(
        'x1c:Q',x2='x2c:Q',y=alt.Y('y1c:Q',axis=None
            )
).transform_calculate(
    x1c='0',x2c=str(slope_chart_width),y1c='1'
)

columns = sorted(data.columns.unique())

#print(columns)

# data_wide = data.pivot(index='date_time',columns=['dilation'])

#print(data_wide)

#print(data_wide.shape)

slope_background = slope_base.transform_pivot(
    'date_time',#groupby=['dilation',],value='dilation',op='values'
).mark_rect(
    color='gray',opacity=0.05,clip=True
).encode(
    y=alt.Y('y1c:Q',#scale=custom_scale
            ),y2='y2c:Q',x=alt.X('x1c:Q',axis=None),tooltip=[# alt.Tooltip('value_3:N',title='Absolut 2')
             ],).transform_calculate(
    y1c='0',y2c=str(slope_chart_height),x1c='0',# value_3= f"if(datum.dilation == 'PRE',datum[datum.dilation == 'PRE'].value,datum[datum.dilation == 'POST'].value)"
       
)

# slope_background

final_slope_chart = (slope_ruler + slope_line + slope_points).resolve_scale(
    x='shared',color='shared'
).resolve_axis(
    x='shared'
)


final_slope_chart = (slope_background + final_slope_chart).resolve_scale(
    y='shared'
).resolve_axis(
    y='independent'
)


final_slope_chart = final_slope_chart.facet(
    facet=alt.Facet('date_time:T',title='',header=alt.Header(format="%Y-%m-%d",formatType='time')),title=''
)

final_slope_chart