optimized_custom_link_walking_in_riak.rb

# Following http://gist.github.com/472547
# If links are already in the 'b2' objects, then getting the top 5 can be done in the first map function

results = Riak::MapReduce.new(client).
            add('b1', 'a').
            link({:bucket => 'b2', :tag => '_', :keep => false}).
            # This first map only emits 5 items instead of all of them
            map("function(v, keydata, arg) { return v.not_found ? [] : JSON.parse(v.values[0].data).links.map(function(x) { return [arg, x]; }).slice(0, 5); }", :keep => false, :arg => 'b3').
            # The following map did not get the 5 items in the correct order ...
            map("function(v) { item = JSON.parse(v.values[0].data); return [item]; }", :keep => false).
            # ... so a reduce is still necessary (but hey, it's just 5 items)
            reduce("function(values, arg) { return values.sort(function(a, b) { if (a.date > b.date) { return -1; } else { return 1 } } ); }", :keep => true).
            timeout(120).
            run