Comments on: MapReduce http://programmingpraxis.com/2009/10/06/mapreduce/ A collection of etudes, updated weekly, for the education and enjoyment of the savvy programmer Mon, 28 May 2012 03:30:45 +0000 hourly 1 http://wordpress.com/ By: Remco Niemeijer http://programmingpraxis.com/2009/10/06/mapreduce/#comment-660 Tue, 06 Oct 2009 17:41:00 +0000 http://programmingpraxis.com/?p=1372#comment-660 My Haskell solution (see http://bonsaicode.wordpress.com/2009/10/06/programming-praxis-mapreduce/ for a version with comments):

mapReduce :: Ord k => (a -> (k, v)) -> (v -> v -> v) ->
                      (k -> k -> Bool) -> [a] -> [(k, v)]
mapReduce m r lt = sortBy (\(a,_) (b,_) -> if lt a b then LT else GT) .
                   M.assocs . M.map (foldl1 r) .
                   M.fromListWith (++) . map (second return . m)

mapReduceInput :: Ord k => (a -> (k, v)) -> (v -> v -> v) ->
    (k -> k -> Bool) -> (String -> [a]) -> FilePath -> IO [(k, v)]
mapReduceInput m r lt g = fmap (mapReduce m r lt . g) . readFile
]]> By: Programming Praxis – MapReduce « Bonsai Code http://programmingpraxis.com/2009/10/06/mapreduce/#comment-659 Tue, 06 Oct 2009 17:40:45 +0000 http://programmingpraxis.com/?p=1372#comment-659 [...] Praxis – MapReduce By Remco Niemeijer In today’s Programming Praxis exercise, we have to implement the famous MapReduce algorithm. Let’s get [...]

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