[Haskell-beginners] Code help requested

[David Frey]

On January 11, 2010 5:22:49 pm Joe Van Dyk wrote:
> I've written two versions of the same program, one in ruby and one in
> haskell.  Given words on stdin, find all the anagrams in those words.
> For nicer display, we're only going to display the top 3 results.
> 
> I'm obviously new to haskell.  The ruby version runs about 5x as fast
> on a large file.   How can I improve the haskell version?
> 
> http://gist.github.com/274774
> 
> # Ruby version
> input = STDIN.read.split("\n")
> result = Hash.new([])
> input.each do |word|
>   sorted_word = word.split('').sort.join
>   result[sorted_word] += [word]
> end
> values = result.values.sort { |a, b| b.size <=> a.size }
> p values[0..3]
> 
> # Haskell version
> import List
> import qualified Data.Map as Map
> 
> -- Given as stdin
> -- presents
> -- serpents
> -- no
> -- on
> -- whatever
> -- Expected Output:
> -- [["serpents","presents"],["on","no"]]
> 
> -- This version only displays words that have more than one
> -- match in the list, and sorts by the words that got the most matches.
> 
> -- Can we do the map bit better?
> 
> main = do
>   input <- getContents
>   print $ anagrams $ lines input
> 
> anagrams words =
>   sorted_anagrams
>   where
>     sorted_anagrams = sortBy sorter filtered_anagrams
>     sorter a b = compare (length b)  (length a)
>     filtered_anagrams = Map.elems $ Map.filter filter_function all_anagrams
>     filter_function words = length words > 1
>     all_anagrams = do_anagrams words Map.empty
>     do_anagrams [] result = result
>     do_anagrams words result = do_anagrams
>                                  (tail words)
>                                  (Map.unionWith
>                                    (++)
>                                    (Map.fromList
> [(sorted_current_word, [current_word])])
>                                    result)
>       where
>         current_word = head words
>         sorted_current_word = sort current_word
> 


Can you provide a link to the data you are using as input?  I ran your program 
over a list of 15000 words and it finished in 0.4 seconds.