3 ms·
And here's the equivalent Ruby program. In Ruby it is usually 'collect' and 'inject' instead of 'map' and 'reduce'. result = Dir.glob('test?.txt').collect
by wedesoft 15y ago
And here's the equivalent Ruby program. In Ruby it is usually 'collect' and 'inject' instead of 'map' and 'reduce'.
result = Dir.glob('test?.txt').collect do |file_name|
File.new(file_name, 'r').read.split(' ').collect do |word|
word.downcase.tr '.,\'', ''
end.inject Hash.new(0) do |hash,word|
hash[word] += 1
hash
end
end.inject do |all,hash|
(all.keys + hash.keys).uniq.inject Hash.new(0) do |acc,word|
acc[word] = all[word] + hash[word]
acc
end
end
p result
Edit: The Python example in the article is better because it merges hashes in the reduce step which facilitates parallelisation.
- cdcarter 15y agoYou can also use Enumerable#map and Enumerable#reduce, to use names that match the pattern (and #map is arguably more idiomatic than #collect).
- chrismealy 15y agoI finally got inject() when they added the reduce() alias.
- cdcarter 15y agoThe thing that confused me most about #inject was the term 'memo'...
- deleted 15y ago[deleted]
- Dn_Ab 15y agoIf i understand correctly collect is more like map from functional programing languages and inject is a fold. One maps a collection of one type to a collection of another type, and the other reduces a collection of one type into something of another type (which could be a collection itself) in that case MapReduce does not quite translate to ruby's collect and inject. In fancy language the reduce in MapReduce is not merely a catamorphism nor is the map actually a collect. The types do not align. I learned of his from a hackernews post by grav1tas http://news.ycombinator.com/item?id=2477238 http://news.ycombinator.com/item?id=2477238. In there he links to a paper: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.104.5859 http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.104.... If you look at the types implicit in his code you should see that the essence lies not with collect or inject which are incidental plumbing but the nature of the hash and in particular, the act of generating the intermediate collection for each key. What is called map is actually more a reverse reduce. The pedagogical emphasis on map and foldr actually belies the true nature and power of algorithm in parallelizing.
- deleted 15y ago[deleted]
- deleted 15y ago[deleted]
- peteretep 15y agoHere's a Perl implementation: use strict; use warnings; use List::Util qw(reduce); use File::Slurp qw(read_file); sub word_count { reduce { $a->{$b}++; $a } {}, map { split(/\W+/) } map { lc read_file $_ } @_; }
- strmpnk 15y agoKind of a odd example just to use map/reduce where each works just fine: result = Hash.new(0) Dir['test?.txt'].each do |file| File.read(file).split(' ').each {|word| result[word.downcase.tr('.,\'', '')] += 1} end If you really needed map/reduce here you'd probably want to write it this way: Dir['test?.txt'].map do |file| Hash.new(0).tap {|result| File.read(file).split(' ').each {|word| result[word.downcase.tr('.,\'', '')] += 1}} end.reduce do |result, partial| result.merge(partial) {|k, v1, v2| v1 + v2} end
- wedesoft 15y agoInteresting. I didn't know that you could pass a block to merge.