def make_preference_space(raw_data, start):
	
	""" create preference_space from raw data

		Args:
			raw_data
			start

		Returns:
			dict: keys are users and values are dictionaries of items and ratings
	"""
	preference_space = {}
	for row in range(0,raw_data.nrows):	
		preference_space[str('user ' + str(start + row))] = {}	
		for col in range(1,raw_data.ncols):
			if raw_data.cell_value(row,col) == 99: continue
			preference_space[str('user ' + str(start + row))]['joke ' + str(col)] = float(raw_data.cell_value(row, col))		
	
	return preference_space