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# The given source file(mappingbased_properties_en.nq) contains input of the form <filed1> <field2> ""<field3> .
# Following is a sample tuple from original input data
# <http://dbpedia.org/resource/United_States_at_the_2004_Summer_Olympics> <http://dbpedia.org/ontology/rankInFinalMedalCount> "1"^^<http://www.w3.org/2001/XMLSchema#positiveInteger> <http://en.wikipedia.org/wiki/United_States_at_the_2004_Summer_Olympics?oldid=490274824#absolute-line=10> .
# Since this tuple is difficult to parse in pig, the preprocessing is done in this file. The above tuple will be
# converted to the form <country>,<year>,<event>,<category>,<rank>
# After preprocessing the above tuple will be United States,2004,Summer_Olympics,rankInFinalMedalCount,1
# NOTE: The reason why we are performing preprocessing here is the join key used for the assignment is country
# and when performing equi-joins the country format should match with second input data set. This preprocessing
# makes sure that the country key conforms to the format of second data set.
# USAGE:
# cat mappingbased_properties_en.nq | ruby etl.rb > output_file
# since this program reads from console and writes back to console, this particular program should take only constant
# memory irrespective of the data size.
# read the input from input file or console
ARGF.each_line do |line|
# we expect the first character to begin with <
next if line[0] != '<'
output = []
line.split("> ").slice(0..2).each_with_index do |word, idx|
if(idx == 0)
val = word[(word.rindex("/")+1)..-1]
validx = val.index("_at_the_")
next if validx == nil
# The join is country and so matching the format of country to match with countries_gdp_2000.csv file
country = val[0..validx-1].gsub('_', ' ')
# extract numbers
year = word.scan(/\d+/).join
event = val.split("_").slice(-2,2)
event = event.join("_")
output.push(country)
output.push(year)
output.push(event)
elsif(idx==1)
category = word[(word.rindex("/")+1)..-1].to_s unless idx==2
output.push(category)
else
rank = word.scan(/"([^"]*)"/).flatten.join unless idx!=2
output.push(rank)
end
end
# though pig handles null values, it is easier to reject nulls or emptry string while preprocessing
output = output.reject { |e| e == nil || e.empty? || e == ""}
next if output.size != 5
# write the output to console
puts output.join(",")
end