legacy structure (I hope)

bind/minipandas.py

@@ -144,19 +144,23 @@ class MiniFrame:
     def copy(self) -> "MiniFrame":
         return MiniFrame({k: v.copy() for k, v in self._data.items()})
 
-    def to_pandas(self):
+    def to_pandas(self, indiv_cols: bool = True):
         import pandas as pd
-        df = pd.DataFrame()
+        out = {}
         for k, v in self._data.items():
             if v.ndim == 1:
-                df[k] = v
-            elif v.ndim == 2:
-                # expand fixed-size vectors into wide columns
+                out[k] = v  # 1D numeric column
+            elif v.ndim == 2 and indiv_cols:
+                # expand into wide columns
                 for i in range(v.shape[1]):
-                    df[f"{k}_{i}"] = v[:, i]
+                    out[f"{k}_{i}"] = v[:, i]
+            elif v.ndim == 2 and not indiv_cols:
+                # legacy nested: one Python list per row (object dtype)
+                # NOTE: v.tolist() -> List[List[...]] which most legacy code expects
+                out[k] = pd.Series(v.tolist(), dtype=object)
             else:
                 raise ValueError(f"Column '{k}' has ndim={v.ndim}, not supported.")
-        return df
+        return pd.DataFrame(out)
 
     # convenience constructor
     @staticmethod