Ch2 page 58 dropping error"['income_cat'] not found in axis"

```python
pd.options.mode.chained_assignment = None
for set_ in (strat_train_set, strat_test_set):
set_.drop("income_cat", axis=1, inplace=True)
```

got the following error..

```
KeyError Traceback (most recent call last)
in
1 pd.options.mode.chained_assignment = None
2 for set_ in (strat_train_set, strat_test_set):
----> 3 set_.drop("income_cat", axis=1, inplace=True)

~\Anaconda3\lib\site-packages\pandas\core\frame.py in drop(self, labels, axis, index, columns, level, inplace, errors)
3695 index=index, columns=columns,
3696 level=level, inplace=inplace,
-> 3697 errors=errors)
3698
3699 @rewrite_axis_style_signature('mapper', [('copy', True),

~\Anaconda3\lib\site-packages\pandas\core\generic.py in drop(self, labels, axis, index, columns, level, inplace, errors)
3109 for axis, labels in axes.items():
3110 if labels is not None:
-> 3111 obj = obj._drop_axis(labels, axis, level=level, errors=errors)
3112
3113 if inplace:

~\Anaconda3\lib\site-packages\pandas\core\generic.py in _drop_axis(self, labels, axis, level, errors)
3141 new_axis = axis.drop(labels, level=level, errors=errors)
3142 else:
-> 3143 new_axis = axis.drop(labels, errors=errors)
3144 result = self.reindex(**{axis_name: new_axis})
3145

~\Anaconda3\lib\site-packages\pandas\core\indexes\base.py in drop(self, labels, errors)
4402 if errors != 'ignore':
4403 raise KeyError(
-> 4404 '{} not found in axis'.format(labels[mask]))
4405 indexer = indexer[~mask]
4406 return self.delete(indexer)

KeyError: "['income_cat'] not found in axis"
```

I checked both the sets with `head()` method and I have the `income_cat` column in them but still I am getting the error. please help.!!