Example of a correlation map

altair/examples/correlation_matrix.py

@@ -0,0 +1,52 @@
+"""
+Correlation matrix
+--------------
+This example shows how to create a correlation matrix and a heatmap from the iris dataset.
+"""
+# category: other charts
+# Load packages
+
+import altair as alt
+from vega_datasets import data
+
+# Load the data
+df_iris = data.iris()
+
+# Create a correlation matrix
+corrMatrix_line = df_iris.corr().round(2).reset_index().rename(columns = {'index':'Var1'}).melt(id_vars = ['Var1'],
+                                                                                                value_name = 'Correlation',
+                                                                                                var_name = 'Var2')
+# Create the heatmap first
+heatmap = alt.Chart(corrMatrix_line).encode(
+    alt.Y('Var1:N', title = ''),
+    alt.X('Var2:N', title = '', axis=alt.Axis(labelAngle=20))
+).mark_rect().encode(
+     alt.Color('Correlation:Q',
+                scale=alt.Scale(scheme='viridis'))
+)
+
+# Add the correlation values as a text mark
+text = heatmap.mark_text(baseline='middle', fontSize=20).encode(
+    text=alt.Text('Correlation:Q', format='.2'),
+    color=alt.condition(
+        alt.datum.Correlation >= 0.95,
+        alt.value('black'),
+        alt.value('white')
+    )
+)
+
+# Set the height, width, title and other properties
+corrMatrix_chart = (heatmap + text).properties(
+    width = 400,
+    height = 400,
+    title = "Iris variables correlation matrix",
+)
+corrMatrix_chart.configure_axis(
+    labelFontSize=18,
+    titleFontSize=24,
+).configure_title(
+    fontSize=24,
+    anchor='start',
+).configure_legend(
+    labelFontSize=20,
+    titleFontSize=20)