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hadoopapache-pig

Pig- Unable to DUMP data

I have two dataset one for movies and other for ratings

Movies Data looks like

MovieID#Title#Genre
1#Toy Story (1995)#Animation|Children's|Comedy
2#Jumanji (1995)#Adventure|Children's|Fantasy
3#Grumpier Old Men (1995)#Comedy|Romance

Ratings Data looks like 

UserID#MovieID#Ratings#RatingsTimestamp
1#1193#5#978300760
1#661#3#978302109
1#914#3#978301968

My Script is as follows

    1) movies_data = LOAD '/user/admin/MoviesDataset/movies_new.dat' USING PigStorage('#') AS (movieid:int,
    moviename:chararray,moviegenere:chararray);

    2) ratings_data = LOAD '/user/admin/RatingsDataset/ratings_new.dat' USING PigStorage('#') AS (Userid:int,
    movieid:int,ratings:int,timestamp:long);

    3) moviedata_ratingsdata_join = JOIN movies_data BY movieid, ratings_data BY movieid;

    4) moviedata_ratingsdata_join_group = GROUP moviedata_ratingsdata_join BY movies_data.movieid;

    5) moviedata_ratingsdata_averagerating = FOREACH moviedata_ratingsdata_join_group GENERATE group,
    AVG(moviedata_ratingsdata_join.ratings) AS Averageratings, (moviedata_ratingsdata_join.Userid) AS userid;

    6) DUMP moviedata_ratingsdata_averagerating;

I am getting this error

 2017-03-25 06:46:50,332 [main] ERROR org.apache.pig.tools.pigstats.PigStats - ERROR 0: org.apache.pig.backend.executionengine.ExecException: ERROR 0: Exception while executing (Name: moviedata_ratingsdata_join_group: Local Rearrange[tuple]{int}(false) - scope-95 Operator Key: scope-95): org.apache.pig.backend.executionengine.ExecException: ERROR 0: Exception while executing (Name: moviedata_ratingsdata_averagerating: New For Each(false,false)[bag] - scope-83 Operator Key: scope-83): org.apache.pig.backend.executionengine.ExecException: ERROR 0: Scalar has more than one row in the output. 1st : (1,Toy Story (1995),Animation|Children's|Comedy), 2nd :(2,Jumanji (1995),Adventure|Children's|Fantasy) (common cause: "JOIN" then "FOREACH ... GENERATE foo.bar" should be "foo::bar" )

If remove line 6, script executes successfully

Why can't I DUMP relation that generates in line 5?

Solution

  • Use the disambiguate operator ( :: ) to identify field names after JOIN, COGROUP, CROSS, or FLATTEN operators.

    Relations movies_data and ratings_data both have a column movieid. When forming relation moviedata_ratingsdata_join_group, Use the :: operator to identify which column movieid to use for GROUP.

    So your 4) would look like,

    4) moviedata_ratingsdata_join_group = GROUP moviedata_ratingsdata_join BY movies_data::movieid;