class_docstr: Create exogeneous features which are a copy of the endogenous data.
  
  Replaces exogeneous features (`X`) by endogeneous data (`y`).
  
  To *add* instead of *replace*, use `FeatureUnion`.
  
  Parameters
  ----------
  subset_index : boolean, optional, default=False
      if True, subsets the output of `transform` to `X.index`,
      i.e., outputs `y.loc[X.index]`
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code: def __init__(self, subset_index=False):
      self.subset_index = subset_index
  
      super().__init__()
  
imports: from sktime.transformations.base import BaseTransformer
label_desc: Use image node_id 1 to create a new YtoX object from inherited base classes: BaseTransformer with example: obj = YtoX(subset_index)