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

Joe Bowbeer joe.bowbeer at gmail.com
Thu Jan 10 10:28:14 PST 2013

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> 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.

More information about the lambda-libs-spec-observers mailing list