code: def scorer(p, y):
      return np.mean(p - y)
  
imports: import numpy
  from mlens.testing import Data, EstimatorContainer
  from mlens.parallel import Group, Learner, Pipeline, run
  from mlens.utils.dummy import OLS, Scale
  from mlens.externals.sklearn.base import clone
label_desc: Use image node_id 1 for calling a global function with example usage: scorer(p, y) and returns: np