added sample size to filter text

plots.py

@@ -98,7 +98,11 @@ class QualtricsPlotsMixin:
         return "_".join(parts)
 
     def _get_filter_description(self) -> str:
-        """Generate a human-readable description of active filters."""
+        """Generate a human-readable description of active filters.
+        
+        Includes sample size (from _last_sample_size) prepended to the filter text.
+        Format: "Sample size: <n> | Filters: ..." or "Sample size: <n>" if no filters.
+        """
         parts = []
         
         # Mapping of attribute name to (display_name, value, options_attr)
@@ -137,12 +141,21 @@ class QualtricsPlotsMixin:
             val_str = ", ".join(clean_values)
             # Use UPPERCASE for category name to distinguish from values
             parts.append(f"{display_name.upper()}: {val_str}")
-            
+        
+        # Get sample size (stored by _ensure_dataframe)
+        sample_size = getattr(self, '_last_sample_size', None)
+        sample_prefix = f"Sample size: {sample_size}" if sample_size is not None else ""
+        
         if not parts:
-            return ""
+            # No filters active - return just sample size (or empty string if no sample size)
+            return sample_prefix
             
         # Join with clear separator - double space for visual break
-        return "Filters:  " + "  —  ".join(parts)
+        filter_text = "Filters:  " + "  —  ".join(parts)
+        
+        if sample_prefix:
+            return f"{sample_prefix}  |  {filter_text}"
+        return filter_text
 
     def _add_filter_footnote(self, chart: alt.Chart) -> alt.Chart:
         """Add a footnote with active filters to the chart.
@@ -248,13 +261,19 @@ class QualtricsPlotsMixin:
         return chart
 
     def _ensure_dataframe(self, data: pl.LazyFrame | pl.DataFrame | None) -> pl.DataFrame:
-        """Ensure data is an eager DataFrame, collecting if necessary."""
+        """Ensure data is an eager DataFrame, collecting if necessary.
+        
+        Also stores the sample size on self._last_sample_size for use in filter descriptions.
+        """
         df = data if data is not None else getattr(self, 'data_filtered', None)
         if df is None:
              raise ValueError("No data provided and self.data_filtered is None.")
         
         if isinstance(df, pl.LazyFrame):
-            return df.collect()
+            df = df.collect()
+        
+        # Store sample size for filter description
+        self._last_sample_size = df.height
         return df
 
     def _clean_voice_label(self, col_name: str) -> str: