pigscript error not calculation max

Question

我遇到了一個豬腳本的問題，我嘗試了很多不同的方法。任何人都可以指出我究竟做錯了什麼？它應該是非常簡單的，我試圖在計算平均值後得到最大值。

a = LOAD 'default.books' using org.apache.hcatalog.pig.HCatLoader(); 
b = LOAD 'default.book_rating' using org.apache.hcatalog.pig.HCatLoader(); 

books_and_ratings = join a by isbn, b by isbn; 

by_isbn = GROUP books_and_ratings BY (a::isbn); 

DESCRIBE by_isbn; 

average_book_rating = FOREACH by_isbn 
     GENERATE books_and_ratings.book_title, books_and_ratings.a::isbn as isbn1, 
     books_and_ratings.book_author, books_and_ratings.publisher, 
     AVG(books_and_ratings.book_rating) as AVG_RATING; 

DESCRIBE average_book_rating; 

group_avg = GROUP average_book_rating ALL; 

DESCRIBE group_avg; 

max_avg_rating = FOREACH group_avg 
    GENERATE FLATTEN average_book_rating.a::book_title, isbn1, 
      average_book_rating.a::book_author, average_book_rating.a::publisher, MAX(AVG_RATING); 

dump max_avg_rating; 

解析失敗：不匹配的輸入 'average_book_rating' 期待LEFT_PAREN

Answer 1

你可以嘗試這樣的。

max_avg_rating = ORDER average_book_rating BY AVG_RATING DESC; 
top_most_rating = LIMIT max_avg_rating 1; 
dump top_most_rating; 

Answer 2

看到閻王最新評論後（「可以有多種書籍最高平均等級」），我想你需要另一組，第一個，獲得通過書號哪些羣體的收視率，你想要的東西之後。

開始是這樣的：由AVG_RATING

grouped_rating = GROUP average_book_rating;

然後你可以使用像@ Sivasakthi代碼：

ordered_avg_rating = ORDER BY grouped_rating DESC組;
top_most_rating = LIMIT ordered_avg_rating 1;
dump top_most_rating;

這樣一來，如果有與平等，最高收視多個結果，top_most_rating將所有的信息接受這個最高等級的書袋。當然，如果你不想把它作爲一個包，你可以把它設計得更方便些。

UPDATE：

這是我怎麼會改變上面的代碼。有一件事情不是純粹的功能，我會首先將評分平均，然後加入書籍/作者信息 - 這會更好地表現明智，否則你會增加評分的大小（其中有很多）時，他們去了。

所以它看起來像這樣：

-- assume a: book_title, isbn, book_author, publisher (and maybe more, which we'll ignore) 
    a = LOAD 'default.books' using org.apache.hcatalog.pig.HCatLoader(); 

    -- assume b: isbn, book_rating (and maybe more, which we'll ignore) 
    b = LOAD 'default.book_rating' using org.apache.hcatalog.pig.HCatLoader(); 

    by_isbn = GROUP b BY isbn; 

    average_book_rating = FOREACH by_isbn GENERATE AVG(b.book_rating) AS AVG_RATING, group AS isbn; 

    group_avg = GROUP average_book_rating BY AVG_RATING; 

    ordered_avg_rating = ORDER group_avg BY group DESC; 

    top_most_rating = LIMIT ordered_avg_rating 1; 

    b = FOREACH top_most_rating GENERATE flatten(average_book_rating); 

    -- now add the book information 

    books_and_ratings = JOIN a BY isbn, b BY isbn; 

    books_and_ratings = FOREACH books_and_ratings GENERATE a::book_title AS title, a::isbn AS isbn, a::book_author AS author,a::publisher AS publisher, b::average_book_rating::AVG_RATING AS max_rating; 

希望這個作品送給你。