Write correct tableSize attribute on index groups for new sequences

src/exdf/write/sd_writer.py

@@ -211,6 +211,12 @@ class SourceDataWriter:
             for path, attrs in attrs.items():
                 source.key[path].attrs.update(attrs)
 
+            # Update tableSize for each index group to the correct
+            # number of trains.
+            for index_group in sd.index_groups:
+                source[index_group].attrs['tableSize'] = sd.data_counts(
+                    labelled=False, index_group=index_group).sum()
+
         # Copy INSTRUMENT data.
         for sd in sources:
             source = f.source[sd.source]