class_docstr: Select Operator
  
  Parameters
  ----------
  feature_left : Expression
      feature instance, select condition
  feature_right : Expression
      feature instance, select value
  
  Returns
  ----------
  feature:
      value(feature_right) that meets the condition(feature_left)
class_docstr_tok: ["Select","Operator","Parameters","--","--","--","--","--","feature_left",":","Expression","feature","instance",",","select","condition","feature_right",":","Expression","feature","instance",",","select","value","Returns","--","--","--","--","--","feature",":","value","(","feature_right",")","that","meets","the","condition","(","feature_left",")"]
code: def _load_internal(self, instrument, start_index, end_index, freq):
      series_condition = self.feature_left.load(
          instrument, start_index, end_index, freq
      )
      series_feature = self.feature_right.load(
          instrument, start_index, end_index, freq
      )
      return series_feature.loc[series_condition]
  
imports: import numpy
  import pandas
  from datetime import datetime
  from qlib.data.cache import H
  from qlib.data.data import Cal
  from qlib.data.ops import ElemOperator, PairOperator
  from qlib.utils.time import time_to_day_index
label_desc: Use image node_id 1 for calling the Select obj's underlying member method code with example usage: obj._load_internal(instrument, start_index, end_index, freq) and returns: series_feature