code: def required_event_fields(next_value_columns, previous_value_columns):
      """
      Compute the set of resource columns required to serve
      ``next_value_columns`` and ``previous_value_columns``.
      """
      # These metadata columns are used to align event indexers.
      return {
          TS_FIELD_NAME,
          SID_FIELD_NAME,
          EVENT_DATE_FIELD_NAME,
      }.union(
          # We also expect any of the field names that our loadable columns
          # are mapped to.
          viewvalues(next_value_columns),
          viewvalues(previous_value_columns),
      )
  
imports: import numpy
  import pandas
  from six import viewvalues
  from toolz import groupby, merge
  from .base import PipelineLoader
  from catalyst.pipeline.common import EVENT_DATE_FIELD_NAME, SID_FIELD_NAME, TS_FIELD_NAME
  from catalyst.pipeline.loaders.frame import DataFrameLoader
  from catalyst.pipeline.loaders.utils import next_event_indexer, previous_event_indexer
label_desc: Use image node_id 1 for calling a global function with example usage: required_event_fields(next_value_columns, previous_value_columns) and returns: unknown