[bug] Chapter 2 Exercise 6

### Enter the chapter number

Chapter 2 Exercise 6

### Enter the page number

_No response_

### What is the cell's number in the notebook

164

### Enter the environment you are using to run the notebook

None

### Describe your issue

class StandardScalerClone(TransformerMixin, BaseEstimator):
def __init__(self, with_mean=True): # no *args or **kwargs!
self.with_mean = with_mean

**def fit(self, X, y=None):
X = validate_data(self, X, ensure_2d=True)
self.n_features_in_ = X.shape[1]
if self.with_mean:
self.mean_ = np.mean(X, axis=0)
self.scale_ = np.std(X, axis=0, ddof=0)
self.scale_[self.scale_ == 0] = 1 # Avoid division by zero
return self**

def transform(self, X):
check_is_fitted(self)
X = validate_data(self, X, ensure_2d=True, reset=False)
if self.with_mean:
X = X - self.mean_
return X / self.scale_

def inverse_transform(self, X):
check_is_fitted(self)
X = validate_data(self, X, ensure_2d=True, reset=False)
return X * self.scale_ + self.mean_

def get_feature_names_out(self, input_features=None):
if input_features is None:
return getattr(self, "feature_names_in_",
[f"x{i}" for i in range(self.n_features_in_)])
else:
if len(input_features) != self.n_features_in_:
raise ValueError("Invalid number of features")
if hasattr(self, "feature_names_in_") and not np.all(
self.feature_names_in_ == input_features
):
raise ValueError("input_features ≠ feature_names_in_")
return input_features

I think we need to assign feature_names_in in the fit function as per the exercise?

### Enter what you expected to happen

_No response_

### If you found a workaround, describe it here

_No response_