Word Count program in Hive

问题:

I'm trying to learn Hive. Surprisingly, I can't find an example of how to write a simple word count job. Is the following correct?

Let's say I have an input file input.tsv:

hello, world
this is an example input file

I create a splitter in Python to turn each line into words:

import sys

for line in sys.stdin:
 for word in line.split():
   print word

And then I have the following in my Hive script:

CREATE TABLE input (line STRING);
LOAD DATA LOCAL INPATH 'input.tsv' OVERWRITE INTO TABLE input;

-- temporary table to hold words...
CREATE TABLE words (word STRING);

add file splitter.py;

INSERT OVERWRITE TABLE words 
  SELECT TRANSFORM(text) 
    USING 'python splitter.py' 
    AS word
  FROM input;

SELECT word, count(*) AS count FROM words GROUP BY word;

I'm not sure if I'm missing something, or if it really is this complicated. (In particular, do I need the temporary words table, and do I need to write the external splitter function?)

回答1:

If you want a simple one see the following:

SELECT word, COUNT(*) FROM input LATERAL VIEW explode(split(text, ' ')) lTable as word GROUP BY word;

I use a lateral view to enable the use of a table valued function (explode) which takes the list that comes out of split function and outputs a new row for every value. In practice I use a UDF that wraps IBM's ICU4J word breaker. I generally don't use transform scripts and use UDFs for everything. You don't need a temporary words table.

回答2:

CREATE TABLE docs (line STRING);
LOAD DATA INPATH 'text' OVERWRITE INTO TABLE docs;
CREATE TABLE word_counts AS
SELECT word, count(1) AS count FROM
(SELECT explode(split(line, '\s')) AS word FROM docs) w
GROUP BY word
ORDER BY word;

回答3:

You may sentences built-in UDF in hive as follows:

1) Step 1: Create a temp table with a single column named sentence of data type array

create table temp as select sentence from docs lateral view explode(explode(sentences(lcase(line)))) ltable as sentence

2) Step 2: Select your words from the temp table again exploding the column sentence

select words,count(words) CntWords from
(
select explode(words) words from temp
) i group by words order by CntWords desc