check_inverse_transform_identity¶

def check_inverse_transform_identity(
    transformer,
    X: pl.DataFrame,
    y: pl.DataFrame | None = None,
    atol: float = 1e-6,
    rtol: float = 1e-5,
) -> None:
    """Check inverse_transform(transform(X)) ≈ X.

    Basic round-trip test for invertible transformers.

    Parameters
    ----------
    transformer : BaseActualTransformer
        Unfitted transformer
    X : pl.DataFrame
        Training data
    y : pl.DataFrame, optional
        Target data
    atol : float
        Absolute tolerance for numerical comparison
    rtol : float
        Relative tolerance for numerical comparison

    Raises
    ------
    AssertionError
        If round-trip fails

    """
    tags = transformer.__sklearn_tags__()
    if not (tags.transformer_tags and tags.transformer_tags.invertible):
        return

    transformer_clone = clone(transformer)
    transformer_clone.fit(X, y)

    # Transform the data - this may drop some rows (e.g., differencing)
    X_trans = transformer_clone.transform(X)

    # For yohou transformers, inverse_transform requires X_p (past observations)
    # immediately preceding X_trans in the original X.
    X_p = _build_X_p(transformer_clone, X, X_trans)

    # Inverse transform
    X_reconstructed = transformer_clone.inverse_transform(X_trans, X_p)

    # The original data we should recover is the portion that was transformed
    # (excluding the dropped rows)
    X_expected = X.tail(len(X_trans))

    # Basic shape check
    assert X_reconstructed.shape == X_expected.shape, (
        f"Shape mismatch: {X_expected.shape} -> {X_trans.shape} -> {X_reconstructed.shape}"
    )

    # Numerical comparison
    assert_frame_equal(X_expected, X_reconstructed, rel_tol=rtol, abs_tol=atol)