Hi Will,
That's partly why I like to use FromCassandraBag and ToCassandraBag from
pygmalion - it does the work for you to get it back into a form that cassandra
understands.
Others may know better how to massage the data into that form using just pig,
but if all else fails, you could write a udf to do that.
Jeremy
On Jun 15, 2011, at 1:17 PM, William Oberman wrote:
> I think I'm stuck on typing issues trying to store data in cassandra. To
> verify, cassandra wants (key, {tuples})
>
> My pig script is fairly brief:
> raw = LOAD 'cassandra://test_in/test_cf' USING CassandraStorage() AS
> (key:chararray, columns:bag {column:tuple (name, value)});
> --colums == timeUUID -> JSON
> rows = FOREACH raw GENERATE key, FLATTEN(columns);
> alias_target_day = FOREACH rows {
> --I wrote a specialized parser that does exactly what I need
> observation_map = com.civicscience.pig.ParseObservation($2);
> GENERATE $0 as alias, observation_map#'_fqt' as target,
> observation_map#'_day' as day;
> };
> grouping = GROUP alias_target_day BY ((chararray)target,(chararray)day);
> X = FOREACH grouping GENERATE group.$0 as target, TOTUPLE(group.$1,
> COUNT($1)) as day_count;
>
> This gets me:
> (targetA, (day1, count))
> (targetA, (day2, count))
> (targetB, (day1, count))
> ....
>
> But, cassandra wants the 2nd item to be a bag. So, I tried:
> X = FOREACH grouping GENERATE group.$0 as target, TOBAG(TOTUPLE(group.$1,
> COUNT($1))) as day_count;
>
> But this results in:
> (targetA, {((day1, count))})
> (targetA, {((day2, count))})
> (targetB, {((day1, count))})
> It's hard to see, but the 2nd item now has a nested tuple as the first value,
> which is still bad.
>
> How to I get (key, {tuple})??? I wasn't sure where to post this (pig or
> cassandra), so I'm posting to the pig list too.
>
> will
