code: def to_vec(self, x):
      if self.one_d:
          return x.flatten()
      else:
          return x.reshape(-1, 1)
  
imports: import dask.dataframe
  import numpy
  import packaging.version
  import pandas
  import pytest
  import sklearn.compose
  import sklearn.pipeline
  import sklearn.preprocessing
  from sklearn.base import BaseEstimator, clone
  import dask_ml.compose
  import dask_ml.preprocessing
  from dask_ml._compat import SK_VERSION
label_desc: Use image node_id 4 for calling the SumTransformer obj's underlying member method code with example usage: obj.to_vec(x) and returns: x, x