"""where mean operation
	filter by equality with a value, then take the mean of (average) the matches
"""
import pandas as pd
import math

SAMPLE = 10

def execute(options, id_columns, value_columns):
	'''
		id_columns - a dictionary mapping names (strings) to numpy arrays
		value_columns - a dictionary mapping names (strings) to numpy arrays

	'''

	columns = id_columns.copy()
	columns.update(value_columns)

	frame = pd.DataFrame(columns)

	id_name = "id_0"
	value_name = "value_0"

	# create a subset of the column values
	column = id_columns[id_name]
	first = column[0]

	#frame.loc[frame[id_name] == 1, value_name].sum()
	v = frame.loc[frame[id_name] == first, value_name].mean()

	return v.item() # convert from numpy type to python type