CODEWITHSUNDEEP
apache-sparkhivehiveqluser-defined-functionshive-udf
martian
martian

Reputation: 23

Hive TRANSFORM receives NULL for concatenated array values

I have a hive table in the format :

   col1.      col2.     col3.
    a1          b1       c1
    a1          b1       c2                                  
    a1          b2       c2
    a1          b2       c3              
    a2          b3       c1
    a2          b4       c1                                  
    a2          b4       c2
    a2          b4       c3              
    .
    .

Every value in col1 can have multiple values in col2 and every such pair of (col1, col2) can have multiple values of col3.

I am running the query [Q]:

select col1, col2, collect_list(col3) from {table} group by col1, col2;

to get:

a1   b1   [c1, c2]
a1   b2   [c2, c3]
a2   b3   [c1]
a2   b4   [c1, c2, c3]

I want to do some transformations using a python UDF. So Im passing all these columns to UDF using TRANSFORM clause as:

select TRANSFORM ( * ) using 'python udf.py' FROM 
(
select col1, col2, concat_ws('\t', collect_list(col3)) from {table} group by col1, col2;
)

I'm using concat_ws to convert the array output to strig from collect_list concatenated by separator. I get col1, col2 in result, but do not get the col3 output.

+---------+---------+
|      key|    value|
+---------+---------+
|a1       | b1      |
|         |     null|
|a1       | b2      |
|         |     null|
|a2       | b3      |
|         |     null|
|a2       | b4      |
|         |     null|
+---------+---------+

In my UDF, I just have a print statement that prints the line received from stdin.

import sys
for line in sys.stdin:
    try:
        print line
    except Exception as e:
        continue

can someone help figure out why i'm not getting the col3 in my UDF ?

Upvotes: 1

Views: 313

Answers (1)

serge_k
serge_k

Reputation: 1772

First, you need to parse the line in Python UDF, e.g.,

import sys
for line in sys.stdin:
    try:
        line = line.strip('\n')
        col1, col2, col3 = line.split('\t')
        print '\t'.join([col1, col2, col3])
    except Exception as e:
        continue

Then it's better to use something else instead of \t in concat_ws

select TRANSFORM ( * )  using 'python udf.py' as (col1, col2, col3)
FROM 
(
select col1, col2, concat_ws(',', collect_list(col3)) from {table} group by col1, col2;

Upvotes: 1

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