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-- Temporal Query Phrase Popularity (Hadoop cluster)

-- This script processes a search query log file from the Excite search engine and compares the occurrence of frequency of search phrases across two time periods separated by twelve hours. 

-- Register the tutorial JAR file so that the included UDFs can be called in the script.
REGISTER ./tutorial.jar;

-- Use the PigStorage function to load the excite log file into the raw bag as an array of records.
-- Input: (user,time,query) 
raw = LOAD 'excite.log.bz2' USING PigStorage('\t') AS (user: chararray, time: chararray, query: chararray);

-- Call the NonURLDetector UDF to remove records if the query field is empty or a URL.
clean1 = FILTER raw BY org.apache.pig.tutorial.NonURLDetector(query);

-- Call the ToLower UDF to change the query field to lowercase.
clean2 = FOREACH clean1 GENERATE user, time, org.apache.pig.tutorial.ToLower(query) as query;

-- Because the log file only contains queries for a single day, we are only interested in the hour.
-- The excite query log timestamp format is YYMMDDHHMMSS.
-- Call the ExtractHour UDF to extract the hour (HH) from the time field.
houred = FOREACH clean2 GENERATE user, org.apache.pig.tutorial.ExtractHour(time) as hour, query;

-- Call the NGramGenerator UDF to compose the n-grams of the query.
ngramed1 = FOREACH houred GENERATE user, hour, flatten(org.apache.pig.tutorial.NGramGenerator(query)) as ngram;

-- Use the DISTINCT command to get the unique n-grams for all records.
ngramed2 = DISTINCT ngramed1;

-- Use the GROUP command to group records by n-gram and hour.
hour_frequency1 = GROUP ngramed2 BY (ngram, hour);

-- Use the COUNT function to get the count (occurrences) of each n-gram.
hour_frequency2 = FOREACH hour_frequency1 GENERATE flatten($0), COUNT($1) as count;

-- Use the FOREACH-GENERATE command to assign names to the fields. 
hour_frequency3 = FOREACH hour_frequency2 GENERATE $0 as ngram, $1 as hour, $2 as count;

-- Use the FILTER command to get the n-grams for hour 00 .
hour00 = FILTER hour_frequency2 BY hour eq '00';

-- Use the FILTER command to get the n-grams for hour 12
hour12 = FILTER hour_frequency3 BY hour eq '12';

-- Use the JOIN command to get the n-grams that appear in both hours.
same = JOIN hour00 BY $0, hour12 BY $0;

-- Use the FOREACH-GENERATE command to record their frequency.
same1 = FOREACH same GENERATE hour00::group::ngram as ngram, $2 as count00, $5 as count12;

-- Use the PigStorage function to store the results. 
-- Output: (n-gram, count_at_hour_00, count_at_hour_12)
STORE same1 INTO 'script2-hadoop-results' USING PigStorage();