code: def generate_string_idx(df, columns, freq_limit, order_by_freq):
      return callZooFunc(
          "float",
          "generateStringIdx",
          df,
          columns,
          freq_limit,
          order_by_freq,
      )
  
imports: from zoo.common.utils import callZooFunc
  from pyspark.sql.types import IntegerType, ShortType, LongType, FloatType, DecimalType, DoubleType
label_desc: Use image node_id 3 for calling a global function with example usage: generate_string_idx(df, columns, freq_limit, order_by_freq) and returns: callZooFunc