class_docstr: Wrapper for a matrix that offers a function to assign the vectors
  to centroids. All other implementations offer the same interface
class_docstr_tok: ["Wrapper","for","a","matrix","that","offers","a","function","to","assign","the","vectors","to","centroids",".","All","other","implementations","offer","the","same","interface"]
code: def __init__(self, x):
      assert x.__class__ == scipy.sparse.csr_matrix
      self.x = x
      self.squared_norms = np.array(x.power(2).sum(1))
  
imports: import numpy
  import faiss
  import time
  from multiprocessing.pool import ThreadPool
label_desc: Use image node_id 1 to create a new DatasetAssignSparse object from inherited base classes: DatasetAssign with example: obj = DatasetAssignSparse(x)