Drawing line plot for a histogram

问题

I'm trying to reproduce this chart using Altair as much as I can. https://fivethirtyeight.com/wp-content/uploads/2014/04/hickey-bechdel-11.png?w=575

I'm stuck at getting the black line dividing pass/fail. This is similar to this Altair example: https://altair-viz.github.io/gallery/step_chart.html. However: in the 538 viz the value for the final date must be extended for the full width of that last element. In the step chart example and my solution, the line stops as soon as the last date element is met.

I have looked at altair's github and google groups and found nothing similar to this problem.

import altair as alt
import pandas as pd

movies=pd.read_csv('https://raw.githubusercontent.com/fivethirtyeight/data/master/bechdel/movies.csv')
domain = ['ok', 'dubious','men', 'notalk', 'nowomen']

base=alt.Chart(movies).encode(
  alt.X("year:N",bin=alt.BinParams(step=5,extent=[1970,2015]),axis=alt.Axis(labelAngle=0, labelLimit=50,labelFontSize=8),title=None),  alt.Y("count()",stack='normalize',title=None,axis=alt.Axis(format='%',values=[0, 0.25,0.50,0.75,1]))

).properties(width=400)
main=base.transform_calculate(cleanrank='datum.clean_test == "ok" ? 1 : datum.clean_test == "dubious" ? 2 : datum.clean_test == "men" ? 3 : datum.clean_test == "notalk" ? 4 : 5'
                ).mark_bar(stroke='white' #add horizontal lines
                ).encode(  
  alt.Color("clean_test:N",scale=alt.Scale(
      domain=domain,
      range=['dodgerblue', 'skyblue', 'pink', 'coral','red']))
    ,order=alt.Order('cleanrank:O', sort='ascending')
)

extra=base.transform_calculate(cleanpass='datum.clean_test == "ok" ? "PASS" : datum.clean_test == "dubious" ? "PASS" : "FAIL"'
                      ).mark_line(interpolate='step-after'
                      ).encode(alt.Color("cleanpass:N",scale=alt.Scale(domain=['PASS','FAIL'],range=['black','white']))
                      )



alt.layer(main,extra).configure_scale(
    bandPaddingInner=0.01 #smaller vertical lines
).resolve_scale(color='independent')

来源：https://stackoverflow.com/questions/57878892/drawing-line-plot-for-a-histogram