滑块截止

此示例展示了如何将可变参数绑定到滑块，以及如何使用相应的绑定值来为数据点着色。此示例基于 Altair 4 文档中关于交互的一个示例，其中交互性是通过选择实现的。以下版本通过使用可变参数得到了显著简化。可变参数是在 Altair 5 中添加的。

方法语法

import altair as alt
import pandas as pd
import numpy as np

rand = np.random.RandomState(42)

df = pd.DataFrame({
    'xval': range(100),
    'yval': rand.randn(100).cumsum()
})

slider = alt.binding_range(min=0, max=100, step=1)
cutoff = alt.param(bind=slider, value=50)
predicate = alt.datum.xval < cutoff

alt.Chart(df).mark_point().encode(
    x='xval',
    y='yval',
    color=alt.when(predicate).then(alt.value("red")).otherwise(alt.value("blue")),
).add_params(
    cutoff
)

属性语法

import altair as alt
import pandas as pd
import numpy as np

rand = np.random.RandomState(42)

df = pd.DataFrame({
    'xval': range(100),
    'yval': rand.randn(100).cumsum()
})

slider = alt.binding_range(min=0, max=100, step=1)
cutoff = alt.param(bind=slider, value=50)
predicate = alt.datum.xval < cutoff

alt.Chart(df).mark_point().encode(
    x='xval',
    y='yval',
    color=alt.when(predicate).then(alt.value("red")).otherwise(alt.value("blue")),
).add_params(
    cutoff
)# No channel encoding options are specified in this chart
# so the code is the same as for the method-based syntax.