Fix cardinality plot for data with string dtypes

sdmetrics/visualization.py

@@ -440,7 +440,7 @@ def _generate_cardinality_plot(
     if plot_type == 'bar':
         max_cardinality = _get_max_between_datasets(real_data, synthetic_data)
         min_cardinality = _get_min_between_datasets(real_data, synthetic_data)
-        plot_kwargs = {'nbins': max_cardinality - min_cardinality + 1}
+        plot_kwargs = {'nbins': int(max_cardinality - min_cardinality + 1)}
 
     return _generate_column_plot(
         real_data, synthetic_data, plot_type, plot_kwargs, plot_title, x_label

tests/unit/test_visualization.py

@@ -5,6 +5,7 @@
 import pandas as pd
 import pytest
 
+from sdmetrics.demos import load_demo
 from sdmetrics.reports.utils import PlotConfig
 from sdmetrics.visualization import (
     _generate_box_plot,
@@ -354,6 +355,33 @@ def test_get_cardinality_plot_bad_plot_type():
         )
 
 
+def test_get_cardinality_plot_with_string_id_columns():
+    """Test ``get_cardinality_plot`` doesn't crash when ID columns have string dtype."""
+    # Setup
+    real_data, synthetic_data, metadata = load_demo(modality='multi_table')
+
+    # cast the primary/foreign columns in the user-sessions relationship to string
+    real_data['users']['user_id'] = real_data['users']['user_id'].astype('string')
+    real_data['sessions']['user_id'] = real_data['sessions']['user_id'].astype('string')
+
+    synthetic_data['users']['user_id'] = synthetic_data['users']['user_id'].astype('string')
+    synthetic_data['sessions']['user_id'] = synthetic_data['sessions']['user_id'].astype('string')
+
+    # Run
+    fig = get_cardinality_plot(
+        real_data=real_data,
+        synthetic_data=synthetic_data,
+        parent_table_name='users',
+        child_table_name='sessions',
+        parent_primary_key='user_id',
+        child_foreign_key='user_id',
+        plot_type='bar',
+    )
+
+    # Assert
+    assert fig is not None
+
+
 def test_get_column_plot_column_not_found():
     """Test the ``get_column_plot`` method when column is not present."""
     # Setup