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

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+"""
+Using Selection Interval with mark_area
+=========================================
+
+Because area is considered one object, just using the plain 
+selector will select the entire area instead of just one part of it.
+
+This example shows how to use two areas, one on top of the other, and a
+`transform_filter` to fake out this effect.
+
+"""
+# category: interactive charts
+import altair as alt
+from vega_datasets import data
+
+source = data.unemployment_across_industries.url
+
+base = alt.Chart(source).mark_area(
+    color='goldenrod',
+    opacity=0.3
+).encode(
+    x='yearmonth(date):T',
+    y='sum(count):Q',
+)
+
+brush = alt.selection_interval(encodings=['x'],empty='all')
+background = base.add_selection(brush)
+selected = base.transform_filter(brush).mark_area(color='goldenrod')
+
+background + selected