how to do Transpose in corresponding few columns in pig/hive

问题

I was wondering is it possible to do transposition corresponding few columns in pig/hive.
as dealing with data i got below requirement

id      jan     feb     march
1       j1      f1      m1
2       j2      f2      m2
3       j3      f3      m3

where i need to transpose it against first column, so it would look like -

id      value   month
1       j1      jan
1       f1      feb
1       m1      march
2       j2      jan
2       f2      feb
2       m2      march
3       j3      jan
3       f3      feb
3       m3      march

I have tried this with java, but to get it into distributed mode is there any way to do it in pig/hive.
appreciating your help in advance!!

回答1:

Pig doesn't have any built-in function to solve your requirement, but you can try the below approach, i guess it will work for you.

input.txt

1       j1      f1      m1
2       j2      f2      m2
3       j3      f3      m3

PigScript:

A = LOAD 'input.txt' USING PigStorage() AS (id,month1,month2,month3);
B = FOREACH A GENERATE FLATTEN(TOBAG(TOTUPLE(id,month1,'jan'),TOTUPLE(id,month2,'feb'),TOTUPLE(id,month3,'mar')));
DUMP B;

Output:

(1,j1,jan)
(1,f1,feb)
(1,m1,mar)
(2,j2,jan)
(2,f2,feb)
(2,m2,mar)
(3,j3,jan)
(3,f3,feb)
(3,m3,mar)

回答2:

Yes this is definitely possible in Hive using the built-in "stack" UDF and a case statement. Something like this should work:

select id, value, CASE
WHEN value like 'j%'
THEN 'jan'
WHEN value like 'f%'
THEN 'feb'
WHEN value like 'm%'
THEN 'march'
ELSE ''
END as month
from table
lateral view stack(3, jan, feb, march) tb as value
;

Let me know if this works.

来源：https://stackoverflow.com/questions/27492700/how-to-do-transpose-in-corresponding-few-columns-in-pig-hive