 sparse matrix} of shape (n_samples, n_features)
    Input data, where `n_samples` is the number of samples and
    `n_features` is the number of features.
    If `precomputed=True`, then `X` is a mask of the input data.

precomputed : bool
    Whether the input data is a mask.

Returns
-------
imputer_mask : {ndarray, sparse matrix} of shape (n_samples,         n_features)
    The imputer mask of the original data.
r