KeyError Traceback (most recent call last) , KeyError: 'Mark' - pandas

Question

Combineddf.plot.scatter(x='Mark', y='Mark2')
---------------------------------------------------------------------------
KeyError Traceback (most recent call last)
~\anaconda3\lib\site-packages\pandas\core\indexes\base.py in get_loc(self, key, method, tolerance)
3628 try:
-> 3629 return self._engine.get_loc(casted_key)
3630 except KeyError as err:
~\anaconda3\lib\site-packages\pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_loc()
~\anaconda3\lib\site-packages\pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_loc()
pandas\_libs\hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()
pandas\_libs\hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()
KeyError: 'Mark'
The above exception was the direct cause of the following exception:
KeyError Traceback (most recent call last)
~\AppData\Local\Temp\ipykernel_4448\4038682785.py in <module>
----> 1 Combineddf.plot.scatter(x='Mark', y='Mark2')
~\anaconda3\lib\site-packages\pandas\plotting\_core.py in scatter(self, x, y, s, c, **kwargs)
1667 ... colormap='viridis')
1668 """
-> 1669 return self(kind="scatter", x=x, y=y, s=s, c=c, **kwargs)
1670
1671 def hexbin(self, x, y, C=None, reduce_C_function=None, gridsize=None, **kwargs):
~\anaconda3\lib\site-packages\pandas\plotting\_core.py in __call__(self, *args, **kwargs)
915 if kind in self._dataframe_kinds:
916 if isinstance(data, ABCDataFrame):
--> 917 return plot_backend.plot(data, x=x, y=y, kind=kind, **kwargs)
918 else:
919 raise ValueError(f"plot kind {kind} can only be used for data frames")
~\anaconda3\lib\site-packages\pandas\plotting\_matplotlib\__init__.py in plot(data, kind, **kwargs)
69 kwargs["ax"] = getattr(ax, "left_ax", ax)
70 plot_obj = PLOT_CLASSES[kind](data, **kwargs)
---> 71 plot_obj.generate()
72 plot_obj.draw()
73 return plot_obj.result
~\anaconda3\lib\site-packages\pandas\plotting\_matplotlib\core.py in generate(self)
327 self._compute_plot_data()
328 self._setup_subplots()
--> 329 self._make_plot()
330 self._add_table()
331 self._make_legend()
~\anaconda3\lib\site-packages\pandas\plotting\_matplotlib\core.py in _make_plot(self)
1113 label = None
1114 scatter = ax.scatter(
-> 1115 data[x].values,
1116 data[y].values,
1117 c=c_values,
~\anaconda3\lib\site-packages\pandas\core\frame.py in __getitem__(self, key)
3503 if self.columns.nlevels > 1:
3504 return self._getitem_multilevel(key)
-> 3505 indexer = self.columns.get_loc(key)
3506 if is_integer(indexer):
3507 indexer = [indexer]
~\anaconda3\lib\site-packages\pandas\core\indexes\base.py in get_loc(self, key, method, tolerance)
3629 return self._engine.get_loc(casted_key)
3630 except KeyError as err:
-> 3631 raise KeyError(key) from err
3632 except TypeError:
3633 # If we have a listlike key, _check_indexing_error will raise
KeyError: 'Mark'
It worked before but now the same code gives error.
Expecting output will be a simple scatter plot of the two mark sets