在 Altair 中组合悬停和单击选择

Question

我想在 Altair 绘图中结合悬停和单击选择。下面的代码产生了我想要的结果：默认情况下点大部分是透明的，将鼠标悬停在该点上会增加不透明度，然后单击该点会进一步增加不透明度。我发现这很有用，用户可以将鼠标悬停在某个点上以快速了解结果，然后单击该点以“锁定”选择。虽然我对结果很满意，但该方法似乎有点麻烦，因为我需要为悬停和单击选择定义不同的图表层。如果我可以构造一个多路条件表达式，那么我似乎可以大大简化代码。我尝试将不透明度条件写为 alt.condition(click_selection, CLICK_OPACITY, alt.condition(hover_selection, HOVER_OPACITY, DEFAULT_OPACITY))，但出现错误。有没有一种方法可以简化我的下面的代码以组合悬停和单击选择？

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

a_values = np.arange(1, 4)
x_values = np.linspace(0, 2, 1000)
DEFAULT_OPACITY = 0.3
HOVER_OPACITY = 0.5
CLICK_OPACITY = 1.0

a_df = pd.DataFrame({'a': a_values})

df = pd.DataFrame({
    'a': np.tile(A=a_values, reps=len(x_values)),
    'x': np.repeat(a=x_values, repeats=len(a_values)),
})
df['y'] = df['a'] * np.sin(2 * np.pi * df['x'])

hover_selection = alt.selection_single(
    clear='mouseout',
    empty='none',
    fields=['a'],
    name='hover_selection',
    on='mouseover',
)
click_selection = alt.selection_single(
    empty='none',
    fields=['a'],
    name='click_selection',
    on='click',
)

a_base = alt.Chart(a_df).mark_point(
    filled=True, size=100,
).encode(
    x=alt.X(shorthand='a:Q', scale=alt.Scale(domain=(min(a_values) - 1, max(a_values) + 1))),
    y=alt.Y(shorthand='a:Q', scale=alt.Scale(domain=(min(a_values) - 1, max(a_values) + 1))),
)
a_hover = a_base.encode(
    opacity=alt.condition(hover_selection, alt.value(HOVER_OPACITY), alt.value(DEFAULT_OPACITY))
).add_selection(hover_selection)
a_click = a_base.encode(
    opacity=alt.condition(click_selection, alt.value(CLICK_OPACITY), alt.value(0.0)),
).add_selection(click_selection)

y_base = alt.Chart(df).mark_line().encode(
    x=alt.X(shorthand='x:Q', scale=alt.Scale(domain=(0, 2))),
    y=alt.Y(shorthand='y:Q', scale=alt.Scale(domain=(-3, 3))),
)
y_hover = y_base.encode(
    opacity=alt.value(HOVER_OPACITY),
).transform_filter(hover_selection)
y_click = y_base.encode(
    opacity=alt.value(CLICK_OPACITY),
).transform_filter(click_selection)

alt.hconcat(
    alt.layer(a_hover, a_click),
    alt.layer(y_hover, y_click),
)

Answer 1

VegaLite支持同条件多选，但我觉得写在alt.Condition内是不可能的。但是，您可以看到 alt.Condition returns 一个字典，因此您可以直接通过选择列表来编写它。

这样你可以澄清这一部分

a_base = alt.Chart(a_df).mark_point(
    filled=True, size=100,
).encode(
    x=alt.X(shorthand='a:Q', scale=alt.Scale(domain=(min(a_values) - 1, max(a_values) + 1))),
    y=alt.Y(shorthand='a:Q', scale=alt.Scale(domain=(min(a_values) - 1, max(a_values) + 1))),
)
a_hover = a_base.encode(
    opacity=alt.condition(hover_selection, alt.value(HOVER_OPACITY), alt.value(DEFAULT_OPACITY))
).add_selection(hover_selection)
a_click = a_base.encode(
    opacity=alt.condition(click_selection, alt.value(CLICK_OPACITY), alt.value(0.0)),
).add_selection(click_selection)

像这样：

hover_and_click_condition = {
    'condition': [
        {'selection': 'hover_selection', 'value': HOVER_OPACITY},
        {'selection': 'click_selection', 'value': CLICK_OPACITY}],
     'value': DEFAULT_OPACITY}

a = alt.Chart(a_df).mark_point(
    filled=True, size=100,
).encode(
    x=alt.X(shorthand='a:Q', scale=alt.Scale(domain=(min(a_values) - 1, max(a_values) + 1))),
    y=alt.Y(shorthand='a:Q', scale=alt.Scale(domain=(min(a_values) - 1, max(a_values) + 1))),
    opacity=hover_and_click_condition
).add_selection(hover_selection, click_selection)

对于转换过滤器，您可以重写此部分

y_base = alt.Chart(df).mark_line().encode(
    x=alt.X(shorthand='x:Q', scale=alt.Scale(domain=(0, 2))),
    y=alt.Y(shorthand='y:Q', scale=alt.Scale(domain=(-3, 3))),
)
y_hover = y_base.encode(
    opacity=alt.value(HOVER_OPACITY),
).transform_filter(hover_selection)
y_click = y_base.encode(
    opacity=alt.value(CLICK_OPACITY),
).transform_filter(click_selection)

alt.hconcat(
    alt.layer(a_hover, a_click),
    alt.layer(y_hover, y_click),
)

像这样：

y = alt.Chart(df).mark_line().encode(
    x=alt.X(shorthand='x:Q', scale=alt.Scale(domain=(0, 2))),
    y=alt.Y(shorthand='y:Q', scale=alt.Scale(domain=(-3, 3))),
    opacity=hover_and_click_condition
)

a | (y.transform_filter(click_selection) + y.transform_filter(hover_selection))

在 Altair 中组合悬停和单击选择

Combine hover and click selections in Altair

python

altair

vega-lite