Apache pig 减去两列中的值并使用pig获得新列

我根据我的标准筛选了一堆行。现在我需要两列减去的值，然后对它们进行排序。这些是我至今使用的命令

data = LOAD '/user/imohit01017881/jk/a2dbe50d-c6e5-42e2-8fd0-5386720ce07b_Data.csv' using PigStorage(',') AS  (Country:chararray, CountryCode:chararray, Series:chararray, SeriesCode:chararray,  yr2000: float, yr2001:float, yr2002 :float, yr2003 :float,  yr2004 :float, yr2005:float,  yr2006:float, yr2007:float, yr2008 :float,  yr2009 :float, yr2010:float, yr2011: float, yr2012 :float, yr2013 : float, yr2014 : float, yr2015:float); 

筛选包含请求数据的行：

data = LOAD '/user/imohit01017881/jk/a2dbe50d-c6e5-42e2-8fd0-5386720ce07b_Data.csv' using PigStorage(',') AS  (Country:chararray, CountryCode:chararray, Series:chararray, SeriesCode:chararray,  yr2000: float, yr2001:float, yr2002 :float, yr2003 :float,  yr2004 :float, yr2005:float,  yr2006:float, yr2007:float, yr2008 :float,  yr2009 :float, yr2010:float, yr2011: float, yr2012 :float, yr2013 : float, yr2014 : float, yr2015:float); 

ggdif = FILTER  data by Series == 'Improved sanitation facilities (% of population with access)' 
dump data 

下面的行给了我一个错误：

data = LOAD '/user/imohit01017881/jk/a2dbe50d-c6e5-42e2-8fd0-5386720ce07b_Data.csv' using PigStorage(',') AS  (Country:chararray, CountryCode:chararray, Series:chararray, SeriesCode:chararray,  yr2000: float, yr2001:float, yr2002 :float, yr2003 :float,  yr2004 :float, yr2005:float,  yr2006:float, yr2007:float, yr2008 :float,  yr2009 :float, yr2010:float, yr2011: float, yr2012 :float, yr2013 : float, yr2014 : float, yr2015:float); 

sub_data = FOREACH ggdif GENERATE SUBTRACT(yr2015, yr2000); 

：SUBTRACT将两个包作为参数，并返回由第一个包（不在第二个包中）的元组组成的新包。 如果为null，则包参数将替换为空包

data = LOAD '/user/imohit01017881/jk/a2dbe50d-c6e5-42e2-8fd0-5386720ce07b_Data.csv' using PigStorage(',') AS  (Country:chararray, CountryCode:chararray, Series:chararray, SeriesCode:chararray,  yr2000: float, yr2001:float, yr2002 :float, yr2003 :float,  yr2004 :float, yr2005:float,  yr2006:float, yr2007:float, yr2008 :float,  yr2009 :float, yr2010:float, yr2011: float, yr2012 :float, yr2013 : float, yr2014 : float, yr2015:float); 

sub_data = FOREACH ggdif GENERATE (yr2015 - yr2000);