Pagerank: Remove duplicate entries from grouping output

[njayaram2]

JIRA: MADLIB-1229
JIRA: MADLIB-1253

Fixes the missing output for complete graphs bug as well.

Co-authored-by: Nandish Jayaram njayaram@apache.org

[asfgit]

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[jingyimei]

The current master has another issue:
When you run

DROP TABLE IF EXISTS vertex, "EDGE";
CREATE TABLE vertex(
id INTEGER
);
CREATE TABLE "EDGE"(
src INTEGER,
dest INTEGER,
user_id INTEGER
);
INSERT INTO vertex VALUES
(0),
(1),
(2);
INSERT INTO "EDGE" VALUES
(0, 1, 1),
(0, 2, 1),
(1, 2, 1),
(2, 1, 1),
(0, 1, 2);


DROP TABLE IF EXISTS pagerank_ppr_grp_out;
DROP TABLE IF EXISTS pagerank_ppr_grp_out_summary;
SELECT pagerank(
'vertex', -- Vertex table
'id', -- Vertix id column
'"EDGE"', -- "EDGE" table
'src=src, dest=dest', -- "EDGE" args
'pagerank_ppr_grp_out', -- Output table of PageRank
NULL, -- Default damping factor (0.85)
NULL, -- Default max iters (100)
NULL, -- Default Threshold 
'user_id');

you will get the following result:

madlib=# select * from pagerank_ppr_grp_out order by user_id, id; user_id | id | pagerank
---------+----+-------------------
1 | 0 | 0.05
1 | 0 | 0.05
1 | 1 | 0.614906399170753
1 | 2 | 0.614906399170753
2 | 0 | 0.075
2 | 1 | 0.13875
(6 rows)

where for user_id=1 the pagerank scores don't sum up to 1 where they should have to. This PR actually fix this issue and gives the right number. However the dev check didn't have a case to catch this issue before. Suggest to add this corner case in dev check to test future changes.

[jingyimei]

See comment.

[njayaram2]

Thank you for the comments @jingyimei , have pushed a commit with a new dev-check test.

[asfgit]

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