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"""
Scatter Plot with LOESS Lines
-----------------------------
This example shows how to add a trend line to a scatter plot using
the LOESS transform (LOcally Estimated Scatterplot Smoothing).
"""
# category: scatter plots
import altair as alt
import pandas as pd
import numpy as np
np.random.seed(1)
source = pd.DataFrame({
'x': np.arange(100),
'A': np.random.randn(100).cumsum(),
'B': np.random.randn(100).cumsum(),
'C': np.random.randn(100).cumsum(),
})
base = alt.Chart(source).mark_circle(opacity=0.5).transform_fold(
fold=['A', 'B', 'C'],
as_=['category', 'y']
).encode(
alt.X('x:Q'),
alt.Y('y:Q'),
alt.Color('category:N')
)
base + base.transform_loess('x', 'y', groupby=['category']).mark_line(size=4)
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