Example of a chart with named thresholds

altair/vegalite/v2/examples/line_chart_with_named_thresholds.py

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+"""
+Line Chart with Named Thresholds
+-------------------
+How to draw thresholds in the chart with a descriptive name.
+"""
+# category: line charts
+import altair as alt
+import pandas as pd
+
+# Games data
+data = [
+    ['2015-04-01', 'Real Madrid', 0],
+    ['2015-04-08', 'Real Madrid', 3],
+    ['2015-04-15', 'Real Madrid', 1],
+    ['2015-04-22', 'Real Madrid', 3],
+    ['2015-04-29', 'Real Madrid', 0],
+    ['2015-05-05', 'Real Madrid', 0],
+    ['2015-05-12', 'Real Madrid', 0],
+    ['2015-05-19', 'Real Madrid', 0],
+    ['2015-04-26', 'Real Madrid', 1],
+    ['2015-06-03', 'Real Madrid', 3],
+    ['2015-04-01', 'Barcelona', 3],
+    ['2015-04-08', 'Barcelona', 0],
+    ['2015-04-15', 'Barcelona', 3],
+    ['2015-04-22', 'Barcelona', 3],
+    ['2015-04-29', 'Barcelona', 3],
+    ['2015-05-05', 'Barcelona', 0],
+    ['2015-05-12', 'Barcelona', 3],
+    ['2015-05-19', 'Barcelona', 1],
+    ['2015-05-26', 'Barcelona', 3],
+    ['2015-06-03', 'Barcelona', 3],
+]
+data = pd.DataFrame(data, columns=['date', 'Team', 'points'])
+
+# The basic line chart
+line = alt.Chart().mark_line().encode(
+    x=alt.X('date:T', title='Games'),
+    y=alt.Y('points:Q', title='Points', 
+            scale=alt.Scale(domain=[-1, 4])),
+    color='Team:N'
+)
+
+thresholds_data = pd.DataFrame([
+    {"th_value": 3, "th": "victory"},
+    {"th_value": 1, "th": "tie"},
+    {"th_value": 0, "th": "defeat"},
+])
+thresholds_rules = alt.Chart(thresholds_data).mark_rule().encode(
+    y='th_value:Q', 
+    opacity=alt.value(0.3)
+)
+thresholds_text = alt.Chart(thresholds_data).mark_text(
+    align='left', dx=-290, dy=-5
+).encode(
+    alt.Y('th_value:Q'),
+    text='th',
+)
+thresholds = thresholds_rules + thresholds_text
+
+alt.layer(line, thresholds, data=data, width=600, height=300).configure_axisY(labels=False)