如何计算pig中不同别名的数据减法？

w46czmvw 于 2021-06-24 发布在 Pig

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dump count_a;
(10)

dump count_b;
(20)

dump count_c;
(30)

现在我要计算：count\u c-count\u b-count\u a。如何在Pig脚本中实现这一点？

1条答案

您需要将这三个别名连接在一起，为此您需要一个公共字段来连接。假设它们都是单记录别名，您可以创建一个字段n来连接：

prep_a = FOREACH count_a GENERATE 1 AS n, a; 
prep_b = FOREACH count_b GENERATE 1 AS n, b; 
prep_c = FOREACH count_c GENERATE 1 AS n, c;

然后您可以通过公共字段n:

ab = JOIN prep_a by n FULL, prep_b by n;
abc = JOIN ab by prep_a::n FULL, prep_c by n;

最后计算出最终结果：

result = FOREACH abc GENERATE (c - b - a) AS result;