code: def median(df, columns, relative_error=0.001):
      return callZooFunc("float", "median", df, columns, relative_error)
  
imports: from zoo.common.utils import callZooFunc
  from pyspark.sql.types import IntegerType, ShortType, LongType, FloatType, DecimalType, DoubleType
label_desc: Use image node_id 8 for calling a global function with example usage: median(df, columns, relative_error) and returns: callZooFunc