Streamlit 中的 Altair 绘图：如何添加图例？

import streamlit as stimport altair as altimport pandas as pddata = pd.DataFrame({"x": [0, 1, 2, 3], "y": [0, 10, 15, 20], "z": [10, 8, 10, 1]})base = alt.Chart(data.reset_index()).encode(x="x")chart = alt.layer(    base.mark_line(color="red").encode(y="y", color=alt.value("green")),    base.mark_line(color="red").encode(y="z", color=alt.value("red")),).properties(title="My plot",)st.altair_chart(chart, theme="streamlit", use_container_width=True)

import streamlit as stimport altair as altimport pandas as pdalt.renderers.enable("html")# Your datadata = pd.DataFrame({    "x": [0, 1, 2, 3],    "y": [0, 10, 15, 20],    "z": [10, 8, 10, 1]})# Transform data to long formatdata_long = pd.melt(data, id_vars=['x'], value_vars=['y', 'z'], var_name='category', value_name='y,z')# Create an Altair chartchart = alt.Chart(data_long).mark_line().encode(    x='x',    y='y,z',    color='category:N'  # Use the category field for color encoding).properties(    title="My plot")st.altair_chart(chart, use_container_width=True)