Join Multiple Relations by Different Fields

[Thomas Bach <th...@students.uni-mainz.de>]

Hi,

Say I have three files `data1`, `data2` and `assocs`:

$ cat data1
key1,foo
key2,bar
$ cat data2
key3,braz
key4,froz
$ cat assoc 
key1,key3
key2,key4

I load these files via

$ pig -b -p debug=WARN -x local
Warning: $HADOOP_HOME is deprecated.

Apache Pig version 0.10.0 (r1328203) compiled Apr 19 2012, 22:54:12
Logging error messages to: /home/vince/tmp/pig_1355407390166.log
Connecting to hadoop file system at: file:///
grunt> data1 = load 'data1' as (key: chararray, val: chararray);  
grunt> data2 = load 'data2' as (key: chararray, val: chararray);  
grunt> assoc = load 'assoc' as (key1: chararray, key2: chararray);

What I want is a relation that looks like:

(foo, braz)
(bar, froz)

That is

data1_val, data1_key <-> assoc_key1, assoc_key2 <-> data2_key, data2_val

So my first assumption was to do a join on data1, assoc first and then
on the resulting relation with data2. Anyways, doing a

A = join data1 by key, assoc by key1;
dump A;

Doesn't yield any results. Is this a bug or am I doing something
conceptually wrong?

Regards,
	Thomas Bach.

Re: Join Multiple Relations by Different Fields

[Jonathan Coveney <jc...@gmail.com>]

it's a little confusing, but the following is a tuple: (key1,foo,)

it's just not the tuple you want. it is a tuple where the first field is
"key1,foo" and the second field is null. The printing makes this ambiguous
2012/12/14 Thomas Bach <th...@students.uni-mainz.de>

> (key1,foo,)

Re: Join Multiple Relations by Different Fields

[Thomas Bach <th...@students.uni-mainz.de>]

Hi all,

I got a hint via StackOverflow[1] the problem was the missing
delimiter definition

On Fri, Dec 14, 2012 at 11:11:43AM +0100, Thomas Bach wrote:
> grunt> data1 = load 'data1' as (key: chararray, val: chararray);  
> grunt> data2 = load 'data2' as (key: chararray, val: chararray);  
> grunt> assoc = load 'assoc' as (key1: chararray, key2: chararray);

this should read

data1 = load 'data1' using PigStorage(',') as (key: chararray, val: chararray);  
data2 = load 'data2' using PigStorage(',') as (key: chararray, val: chararray);  
assoc = load 'assoc' using PigStorage(',') as (key1: chararray, key2: chararray);

I got confused because the original statement yielded

grunt> dump data1;
(key1,foo,)
(key2,bar,)

So I took for granted that this is a tuple…

Sorry for the noise,

      Thomas Bach.

Footnotes: 
[1]  http://stackoverflow.com/questions/13861570/join-multiple-relations-by-different-fields