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.venv/Lib/site-packages/altair/examples/multiline_highlight.py

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+"""
+Multi-Line Highlight
+====================
+This multi-line chart uses an invisible Voronoi tessellation to handle mouseover to
+identify the nearest point and then highlight the line on which the point falls.
+It is adapted from the Vega-Lite example found at
+https://bl.ocks.org/amitkaps/fe4238e716db53930b2f1a70d3401701
+"""
+# category: interactive charts
+import altair as alt
+from vega_datasets import data
+
+source = data.stocks()
+
+highlight = alt.selection(type='single', on='mouseover',
+                          fields=['symbol'], nearest=True)
+
+base = alt.Chart(source).encode(
+    x='date:T',
+    y='price:Q',
+    color='symbol:N'
+)
+
+points = base.mark_circle().encode(
+    opacity=alt.value(0)
+).add_selection(
+    highlight
+).properties(
+    width=600
+)
+
+lines = base.mark_line().encode(
+    size=alt.condition(~highlight, alt.value(1), alt.value(3))
+)
+
+points + lines