Altair mark_text 标签，其中 x 轴中的域被链接

Question

I was trying to give text labels on some altair chart linked to a selected interval from another chart. I realize that the text given by "mark_text ()" doesn't show completely at the last points of the chart where the domain in the x-axis is specified to be the interval selected, also I didn't know how to specify the format so the dates will be given just as yyyy-mm or month-year (don't want to display the day).

Another thing that I realized, is when one specifies the tooltip doesn't show at all when the domain on the x-axis of the graph is also linked to an interval selected in another chart, that's the reason I used the mark_text()
the code I'm using is the following

import altair as alt
from vega_datasets import data

nearest = alt.selection_single(nearest=True, on='mouseover',
                    encodings=['x','y'], empty='none')
interval = alt.selection_interval(encodings=['x'])
weather = data.seattle_weather()
base = alt.Chart(weather).mark_rule(size=2).encode(
x='date:T')

chart = base.mark_line().encode(
x=alt.X('date:T', scale=alt.Scale(domain=interval.ref())),
    y='temp_max:Q',).properties(
width=800,
height=300)

text=base.mark_text(align='left', dx=5, dy=5).encode(
y='temp_max:Q',
text=alt.condition(nearest, 'label:N', alt.value(' '))
).transform_calculate(label='"Date: " + format(datum.date, "") '
                     ).properties(selection=nearest,width=800,
height=300)

point=base.mark_point().encode(y='temp_max:Q',opacity=alt.condition(nearest, alt.value(1), alt.value(0)))



view = base.mark_line().add_selection(
interval).properties(width=800, height=20)


(point+text+chart) &view

Answer 1

It looks like you're trying to create a tooltip using a layer, and this is the cause of many of the problems you're having. Have you considered using the tooltip encoding?

import altair as alt
from vega_datasets import data

nearest = alt.selection_single(nearest=True, on='mouseover',
                    encodings=['x','y'], empty='none')
interval = alt.selection_interval(encodings=['x'])
weather = data.seattle_weather()

line = alt.Chart(weather).mark_line().encode(
    x=alt.X('date:T', scale=alt.Scale(domain=interval)),
    y='temp_max:Q'
).properties(
    width=800,
    height=200
)
point = line.mark_point().encode(
    tooltip='yearmonth(date):N',
    opacity=alt.condition(nearest, alt.value(1), alt.value(0))
).add_selection(nearest)

view = alt.Chart(weather).mark_line().encode(
    x='date:T',
).properties(
    width=800,
    height=20
).add_selection(interval)

(point + line) & view