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"""
Line Chart with Custom Legend
-----------------------------
This example uses the argmax aggregation function in order to create a custom
legend for a line chart.
"""
# category: line charts
import altair as alt
from vega_datasets import data
source = data.stocks()
base = alt.Chart(source).encode(
color=alt.Color("symbol", legend=None)
).transform_filter(
"datum.symbol !== 'IBM'"
).properties(
width=500
)
line = base.mark_line().encode(x="date", y="price")
last_price = base.mark_circle().encode(
x=alt.X("last_date['date']:T"),
y=alt.Y("last_date['price']:Q")
).transform_aggregate(
last_date="argmax(date)",
groupby=["symbol"]
)
company_name = last_price.mark_text(align="left", dx=4).encode(text="symbol")
chart = (line + last_price + company_name).encode(
x=alt.X(title="date"),
y=alt.Y(title="price")
)
chart
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