register datasketches-memory-2.0.0.jar;
register datasketches-java-3.1.0.jar;
register datasketches-pig-1.1.0.jar;
-- very small sketch just for the purpose of this tiny example
DEFINE DataToSketch org.apache.datasketches.pig.sampling.DataToVarOptSketch('4', '0');
DEFINE VarOptUnion org.apache.datasketches.pig.sampling.VarOptUnion('4');
DEFINE GetVarOptSamples org.apache.datasketches.pig.sampling.GetVarOptSamples();
raw_data = LOAD 'data.txt' USING PigStorage('\t') AS
(weight: double, id: chararray);
-- make a few independent sketches from the input data
bytes = FOREACH
(GROUP raw_data ALL)
GENERATE
DataToSketch(raw_data) AS sketch0,
DataToSketch(raw_data) AS sketch1
;
sketchBag = FOREACH
bytes
GENERATE
TOBAG(sketch0,
sketch1)) AS sketches
;
unioned = FOREACH
sketchBag
GENERATE
VarOptUnion(sketchBag.sketches) AS binSketch
;
result = FOREACH
unioned
GENERATE
FLATTEN(GetVarOptSamples(binSketch)) AS (vo_weight, record:(id, weight))
;
DUMP result;
DESCRIBE result;
The test data has 2 fields: weight and id. The first step of the query creates several varopt sketches from the input data. We merge the sketches into a bag in the next step, followed by unioning the set of independent sketches. Finally, the last step gets the final set of results.
Results:
From ‘DUMP result’:
(30.0,(30.0,h))
(30.0,(30.0,h))
(28.0,(4.0,d))
(28.0,(7.0,g))
By running this script repeatedly, we can obesrve that the heavy items (h) will always be included, but that the remaining 2 items will differ across runs, appearing in proportion to their weights. We can also see that the output varopt weight on the non-heavy samples represents an adjusetd weight, although by keeping the entire input tuple the original weight value is also stored.
From ‘DESCRIBE result’:
result: {vo_weight: double,record: (id: bytearray,weight: bytearray)}
1.0 a
2.0 b
3.0 c
4.0 d
5.0 e
6.0 f
7.0 g
30.0 h