Merge pull request #534 from eitanlees/layered-histogram

Layered Histogram Example

altair/vegalite/v2/examples/layered_histogram.py

@@ -0,0 +1,31 @@
+"""
+Layered Histogram
+=================
+This example shows how to make a layered histogram in Altair.
+"""
+
+import pandas as pd
+import altair as alt
+import numpy as np
+np.random.seed(42)
+
+# Generating Data
+df = pd.DataFrame({'Trial A':np.random.normal(0, 0.8, 1000),
+                   'Trial B':np.random.normal(-2, 1, 1000),
+                   'Trial C':np.random.normal(3, 2, 1000)})
+
+# Tidying Data
+df = pd.melt(df, id_vars=df.index.name, 
+             value_vars=df.columns,
+             var_name = 'Experiment',
+             value_name='Measurement')
+
+chart = alt.Chart(df).mark_area(opacity=0.3, interpolate='step').encode(
+    x=alt.X('Measurement',bin = alt.BinParams(maxbins=100)),
+    y=alt.Y('count(*):Q', stack=None), 
+    color=alt.Color('Experiment', 
+                    scale=alt.Scale(range=['#0000ff', 
+                                           '#008000', 
+                                           '#ff0000'])
+                   )
+)