Merge 02fc006 into 9866fda

doc/known-issues.rst

@@ -11,3 +11,9 @@ Known issues
   handles in the MAD-X process or prevent them from being inherited by
   default.  You have to make sure on your own that you close all file handles
   before creating a new ``cpymad.madx.Madx`` instance!
+
+- the MAD-X ``USE`` command invalidates table row names. Therefore, using
+  ``Table.dframe()`` is unsafe after ``USE`` should be avoided, unless
+  manually specifying an index, e.g. ``Table.dframe(index='name')``, see `#93`_.
+
+.. _#93: https://github.com/hibtc/cpymad/issues/93

src/cpymad/madx.py

@@ -1111,7 +1111,13 @@ def col_names(self):
         return self._libmadx.get_table_column_names(self._name)
 
     def row_names(self):
-        """Get table row names."""
+        """
+        Get table row names.
+
+        WARNING: using ``row_names`` after calling ``USE`` (before recomputing
+        the table) is unsafe and may lead to segmentation faults or incorrect
+        results.
+        """
         return self._libmadx.get_table_row_names(self._name)
 
     @property
@@ -1142,10 +1148,28 @@ def copy(self, columns=None) -> dict:
             columns = self
         return {column: self[column] for column in columns}
 
-    def dframe(self, columns=None):
-        """Return table as ``pandas.DataFrame``."""
+    def dframe(self, columns=None, index=None):
+        """
+        Return table as ``pandas.DataFrame``.
+
+        :param list columns: column names or ``None`` for all columns.
+        :param str index: column name or sequence to be used as index, or
+                          ``None`` for using the ``row_names``
+        :returns: column data as ``pandas.DataFrame``
+        :raises ValueError: if the table name is invalid
+
+        WARNING: using ``index=None`` is unsafe after calling ``USE``.
+        In this case, please manually specify another column to be used,
+        e.g. ``index="name"``.
+        """
         import pandas as pd
-        return pd.DataFrame(self.copy(columns), index=self.row_names())
+        if index is None:
+            index = self.row_names()
+        elif isinstance(index, str):
+            index = np.partition(self[index], ':')[:, 0]
+        else:
+            index = index
+        return pd.DataFrame(self.copy(columns), index=index)
 
     def getmat(self, name, idx, *dim):
         s = () if isinstance(idx, int) else (-1,)