How to parse a JSON string from a column with Pig

Question

I have tsv log files where a column is populated by a json string.

I want to parse that column with JsonLoader in a Pig script. I saw many examples where JsonLoader is used in cases where each row is only a json string. I have other columns I want to skip and I don't know how to do that.

The file looks like this:

foo    bar    {"version":1; "type":"an event"; "count": 1}
foo    bar    {"version":1; "type":"another event"; "count": 1}

How can I do that?

Answer 1

You are looking for the JsonStringToMap UDF provided in Elephant Bird: https://github.com/kevinweil/elephant-bird/search?q=JsonStringToMap&ref=cmdform

Sample File:

foo     bar     {"version":1, "type":"an event", "count": 1}
foo     bar     {"version":1, "type":"another event", "count": 1}

Pig Script:

REGISTER /path/to/elephant-bird.jar;
DEFINE JsonStringToMap com.twitter.elephantbird.pig.piggybank.JsonStringToMap();
raw = LOAD '/tmp/file.tsv' USING PigStorage('\t') AS (col1:chararray,col2:chararray,json_string:chararray);
parsed = FOREACH raw GENERATE col1,col2,JsonStringToMap(json_string);
ILLUSTRATE parsed; -- Just to show the output

Pre-processing (JSON as chararray/string):

-------------------------------------------------------------------------------------------------------
| raw     | col1:chararray    | col2:chararray    | json_string:chararray                             | 
-------------------------------------------------------------------------------------------------------
|         | foo               | bar               | {"version":1, "type":"another event", "count": 1} | 

Post-processing (JSON as map):

---

-------------------------------------------------------------------------------------------------
| parsed     | col1:chararray    | col2:chararray    | json:map(:chararray)                     | 
-------------------------------------------------------------------------------------------------
|            | foo               | bar               | {count=1, type=another event, version=1} | 
-------------------------------------------------------------------------------------------------

Here's the same question asked just two days ago: How do you decode JSON in Pig that comes from a column?