v0.5.0 "Half-a-gram"

sbo 0.5.0

API and UI changes

• Former kgram_freqs class is now called sbo_kgram_freqs. The constructor
  kgram_freqs() is still available as an alias to sbo_kgram_freqs().

• Former sbo_preds class is now substituted by two classes:

    - `sbo_predictor`: for interactive use
    - `sbo_predtable`: for storing text predictors out of memory (e.g. 
    `save()` to file)
  

• sbo_predictor and sbo_predtable objects are obtained by the homonym
  constructors, which are now S3 generics accepting character input, as well as
  sbo_kgram_freqs and sbo_predtable (for the sbo_predictor() constructor)
  class objects. In particular, these allow to directly train a text predictor
  without storing the intermediate sbo_dictionary, and kgram_freqs objects.

• The behaviour of the dict argument in kgram_freqs() and kgram_freqs_fast() has changed, now accepting either a sbo_dictionary, a character or a formula (see also 'New features').

• The sbo_predictor implementation dramatically improves the speed of
  predict() (by a factor of x10). A single call to predict() now allocates a
  few kBs of RAM (whereas it previously allocated few MBs, c.f. issue #10).

• Metadata of sbo_kgram_freqs and sbo_pred* objects is now stored via
  attributes (#11).

New features

• New S3 class sbo_dictionary.
• New S3 class word_coverage with generic constructors and a preconfigured
  plot() method.
• Dictionaries in kgram_freqs() and sbo_pred*() can now
  be built also with a fixed target coverage fraction of training corpus.
• Added prune() generic function for reducing -gram order of
  kgram_freqs and sbo_predtable's.
• Added summary() methods for sbo_kgram_freqs and sbo_pred* objects;
  correspondingly, the output of print() has been simplified considerably (#5).
• The object of class sbo_kgram_freqs, sbo_dictionary, sbo_predictor and
  sbo_predtable can be constructed either through the homonymous constructors,
  or through the aliases kgram_freqs(), dictionary(), predictor(),
  predtable().

Other improvements and patches

• sbo now has SystemRequirements: C++11, for correct integration with C++11 code (in particular std::unordered_map).

• Model training (with sbo_predictor()) is now considerably faster, due to
  optimizations in the algorithm for building Stupid Back-Off prediction tables.

• The Stupid Back-Off algorithm is now thoroughly tested, and small
  inconsistencies between the predict.kgram_freqs() and
  predict.sbo_predictor() methods have been fixed, including:

    - Proper handling of unknown words
    - Consistent handling of ties in prediction probabilities.
  

• Model evaluation in eval_sbo_predictor() is now carried out by sampling
  a single sentence from each document in test corpus.

• Removed unnecessary dependencies from Depends and Imports package fields.

v0.3.2

• Patch addressing inexpected behaviour of erase argument in
  preprocess() and get_kgram_freqs_fast(), c.f. issue #17.

sbo 0.3.1

• Changed leading to trailing underscore in private variables definition of C++ kgramFreqs class, as per §1.6.4 of the "Writing R extensions" guide.
• Removed Catch tests infrastructure for C++ code.

First release

• Added get_kgram_freqs_fast() for fast and memory efficient kgram tokenization using the default text preprocessing utility.