Anagrams Kata (Was: ConcurrentHashMap/ConcurrentMap/Map.compute)

[Joe Bowbeer]

Thanks for the suggestions Paul.

After updating to jdk8lambda b72, the anagram collector is now expressed as:

  map = r.lines().accumulate(Accumulators.<String,
String>groupBy(Anagrams::key));

Notes:

1. Adding .parallel() after lines() works, but in my tests on a dual-core
laptop, it increased the accumulate time by an order of magnitude.

2. The Accumulators.<> type specifier is currently required, unfortunately.

The complete source (all 31 lines) is at
bitbucket.org/joebowbeer/anagrams/src/

In my trials, I'm using the long list of single words from
http://icon.shef.ac.uk/Moby/mwords.html

Joe

On Wed, Jan 9, 2013 at 1:15 AM, Paul Sandoz <paul.sandoz at oracle.com> wrote:

>
> On Jan 9, 2013, at 7:47 AM, Joe Bowbeer <joe.bowbeer at gmail.com> wrote:
>
> > In the javadoc for Map.compute in b72, there is an error in the sample
> > snippet:
> >
> > http://download.java.net/lambda/b72/docs/api/java/util/Map.html
> >
> > Attempts to compute a mapping for the specified key and its current
> mapped
> >> value (or null if there is no current mapping). For example, to either
> >> create or append a String msg to a value mapping:
> >> map.compute(key, (k, v, msg) -> (v == null) ? msg : v.concat(msg))
> >
> >
> > Error: BiFunction does not accept three arguments.  In particular, msg is
> > extraneous.  It should be defined in the lexical scope?
> >
> >
> > Btw, I pondered how to efficiently use compute() or merge() to simulate a
> > multi-map and I eventually gave up.
> >
> > I eventually wrote the following, which accumulates lists of anagrams,
> > given a list of words:
> >
> > r.lines().forEach(s -> map.computeIfAbsent(key(s), k -> new
> > ArrayList<>()).add(s));
> >
>
> Have you tried using the latest groupBy functionality? e.g.:
>
>   Map<String, Collection<String>> anagrams =
> r.lines().parallel().reduce(groupBy(s -> key(s)));
>
> It would be interesting to compare performance of reduce vs.
> reduceUnordered and the concurrent groupBy leveraging CHM.
>
>
> >
> > Where key() returns the canonical key for a given word, and r is a
> > BufferedReader for the dictionary file.
> >
> > The following line prints the lists of anagrams:
> >
> > map.values().stream().filter(v -> v.size() > 1).forEach(v ->
> > System.out.println(v));
> >
>
> Little style tip:
>
>   forEach(System.out::println)
>
> Paul.
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