基于测量亮度的带标签的条形图

此示例显示了一个基本的水平条形图，其中的标签根据测量的亮度决定文本覆盖的颜色是 black 还是 white。

Method syntax

import altair as alt
from vega_datasets import data

source = data.barley()

base = alt.Chart(source).encode(
    x=alt.X('sum(yield):Q').stack('zero'),
    y=alt.Y('site:O').sort('-x'),
    text=alt.Text('sum(yield):Q', format='.0f')
)

bars = base.mark_bar(
    tooltip=alt.expr("luminance(scale('color', datum.sum_yield))")
).encode(
    color='sum(yield):Q'
)

text = base.mark_text(
    align='right',
    dx=-3,
    color=alt.expr("luminance(scale('color', datum.sum_yield)) > 0.5 ? 'black' : 'white'")
)

bars + text

Attribute syntax

import altair as alt
from vega_datasets import data

source = data.barley()

base = alt.Chart(source).encode(
    x=alt.X('sum(yield):Q', stack='zero'),
    y=alt.Y('site:O', sort='-x'),
    text=alt.Text('sum(yield):Q', format='.0f')
)

bars = base.mark_bar(
    tooltip=alt.expr("luminance(scale('color', datum.sum_yield))")
).encode(
    color='sum(yield):Q'
)

text = base.mark_text(
    align='right',
    dx=-3,
    color=alt.expr("luminance(scale('color', datum.sum_yield)) > 0.5 ? 'black' : 'white'")
)

bars + text