FSelector: a Ruby gem for feature selection
Source Code: https://github.com/need47/fselector
Publication: Bioinformatics, 2012, 28, 2851-2852
Author: Tiejun Cheng
License: MIT License
Latest Version: 1.4.0
Release Date: 2012-11-05
FSelector is a Ruby gem that aims to integrate various feature selection algorithms and related functions into one single package. Welcome to contact me (firstname.lastname@example.org) if you'd like to contribute your own algorithms or report a bug. FSelector allows user to perform feature selection by using either a single algorithm or an ensemble of multiple algorithms, and other common tasks including normalization and discretization on continuous data, as well as replace missing feature values with certain criterion. FSelector acts on a full-feature data set in either CSV, LibSVM or WEKA file format and outputs a reduced data set with only selected subset of features, which can later be used as the input for various machine learning softwares such as LibSVM and WEKA. FSelector, as a collection of filter methods, does not implement any classifier like support vector machines or random forest. Check below for a list of FSelector's features, ChangeLog for updates, and HowToContribute if you want to contribute.
1. supported input/output file types
- weka ARFF
- on-line dataset in one of the above three formats (read only)
- random data (read only, for test purpose)
2. available feature selection/ranking algorithms
algorithm shortcut algo_type applicability feature_type -------------------------------------------------------------------------------------------------- Accuracy Acc weighting multi-class discrete AccuracyBalanced Acc2 weighting multi-class discrete BiNormalSeparation BNS weighting multi-class discrete CFS_d CFS_d searching multi-class discrete ChiSquaredTest CHI weighting multi-class discrete CorrelationCoefficient CC weighting multi-class discrete DocumentFrequency DF weighting multi-class discrete F1Measure F1 weighting multi-class discrete FishersExactTest FET weighting multi-class discrete FastCorrelationBasedFilter FCBF searching multi-class discrete GiniIndex GI weighting multi-class discrete GMean GM weighting multi-class discrete GSSCoefficient GSS weighting multi-class discrete InformationGain IG weighting multi-class discrete INTERACT INTERACT searching multi-class discrete JMeasure JM weighting multi-class discrete KLDivergence KLD weighting multi-class discrete MatthewsCorrelationCoefficient MCC, PHI weighting multi-class discrete McNemarsTest MNT weighting multi-class discrete OddsRatio OR weighting multi-class discrete OddsRatioNumerator ORN weighting multi-class discrete PhiCoefficient PHI weighting multi-class discrete Power Power weighting multi-class discrete Precision Precision weighting multi-class discrete ProbabilityRatio PR weighting multi-class discrete Recall Recall weighting multi-class discrete Relief_d Relief_d weighting two-class discrete ReliefF_d ReliefF_d weighting multi-class discrete Sensitivity SN, Recall weighting multi-class discrete Specificity SP weighting multi-class discrete SymmetricalUncertainty SU weighting multi-class discrete BetweenWithinClassesSumOfSquare BSS_WSS weighting multi-class continuous CFS_c CFS_c searching multi-class continuous FTest FT weighting multi-class continuous KS_CCBF KS_CCBF searching multi-class continuous KSTest KST weighting two-class continuous PMetric PM weighting two-class continuous Relief_c Relief_c weighting two-class continuous ReliefF_c ReliefF_c weighting multi-class continuous TScore TS weighting two-class continuous WilcoxonRankSum WRS weighting two-class continuous LasVegasFilter LVF searching multi-class discrete, continuous, mixed LasVegasIncremental LVI searching multi-class discrete, continuous, mixed Random Rand weighting multi-class discrete, continuous, mixed RandomSubset RandS searching multi-class discrete, continuous, mixed
note for feature selection interface:
there are two types of filter algorithms: filter_by_feature_weighting and filter_by_feature_searching
- for former: use either select_feature_by_score! or select_feature_by_rank!
- for latter: use select_feature!
3. feature selection approaches
- by a single algorithm
- by multiple algorithms in a tandem manner
- by multiple algorithms in an ensemble manner (share the same feature selection interface as single algorithm)
4. availabe normalization and discretization algorithms for continuous feature
algorithm note --------------------------------------------------------------------------------------- normalize_by_log! normalize by logarithmic transformation normalize_by_min_max! normalize by scaling into [min, max] normalize_by_zscore! normalize by converting into zscore discretize_by_equal_width! discretize by equal width among intervals discretize_by_equal_frequency! discretize by equal frequency among intervals discretize_by_ChiMerge! discretize by ChiMerge algorithm discretize_by_Chi2! discretize by Chi2 algorithm discretize_by_MID! discretize by Multi-Interval Discretization algorithm discretize_by_TID! discretize by Three-Interval Discretization algorithm
5. availabe algorithms for replacing missing feature values
algorithm note feature_type --------------------------------------------------------------------------------------------- replace_by_fixed_value! replace by a fixed value discrete, continuous replace_by_mean_value! replace by mean feature value continuous replace_by_median_value! replace by median feature value continuous replace_by_knn_value! replace by weighted knn feature value continuous replace_by_most_seen_value! replace by most seen feature value discrete
To install FSelector, use the following command:
$ gem install fselector
note: From version 0.5.0, FSelector uses the RinRuby gem (http://rinruby.ddahl.org) as a seemless bridge to access the statistical routines in the R package (http://www.r-project.org), which will greatly expand the inclusion of algorithms to FSelector, especially for those relying on statistical test. To this end, please pre-install the R package. RinRuby should have been auto-installed with FSelector via the above command.
1. feature selection by a single algorithm
require 'fselector' # use InformationGain (IG) as a feature selection algorithm r1 = ::.new # read from random data (or csv, libsvm, weka ARFF file) # no. of samples: 100 # no. of classes: 2 # no. of features: 15 # no. of possible values for each feature: 3 # allow missing values: true r1.data_from_random(100, 2, 15, 3, true) # number of features before feature selection puts " # features (before): "+ r1.get_features.size.to_s # select the top-ranked features with scores >0.01 r1.select_feature_by_score!('>0.01') # number of features after feature selection puts " # features (after): "+ r1.get_features.size.to_s # you can also use a second alogirithm for further feature selection # e.g. use the ChiSquaredTest (CHI) with Yates' continuity correction # initialize from r1's data r2 = ::.new(:yates, r1.get_data) # number of features before feature selection puts " # features (before): "+ r2.get_features.size.to_s # select the top-ranked 3 features r2.select_feature_by_rank!('<=3') # number of features after feature selection puts " # features (after): "+ r2.get_features.size.to_s # save data to standard ouput as a weka ARFF file (sparse format) # with selected features only r2.data_to_weka(:stdout, :sparse)
2. feature selection by an ensemble of multiple feature selectors
require 'fselector' # example 1 # # creating an ensemble of feature selectors by using # a single feature selection algorithm (INTERACT) # by instance perturbation (e.g. random sampling) # test for the type of feature subset selection algorithms r = ::.(0.0001) # an ensemble of 40 feature selectors with 90% data by random sampling re = ::.(r, 40, 0.90, :random_sampling) # read SPECT data set (under the test/ directory) re.data_from_csv('test/SPECT_train.csv') # number of features before feature selection puts ' # features (before): ' + re.get_features.size.to_s # only features with above average count among ensemble are selected re.select_feature! # number of features after feature selection puts ' # features before (after): ' + re.get_features.size.to_s # example 2 # # creating an ensemble of feature selectors by using # two feature selection algorithms: InformationGain (IG) and Relief_d. # note: can be 2+ algorithms, as long as they are of the same type, # either filter_by_feature_weighting or filter_by_feature_searching # test for the type of feature weighting algorithms r1 = ::.new r2 = ::.(10) # an ensemble of two feature selectors re = ::.(r1, r2) # read random discrete data (containing missing value) re.data_from_random(100, 2, 15, 3, true) # replace missing value because Relief_d # does not allow missing value re.replace_by_most_seen_value! # number of features before feature selection puts ' # features (before): ' + re.get_features.size.to_s # based on the max feature score (z-score standardized) among # an ensemble of feature selectors re.ensemble_by_score(:by_max, :by_zscore) # select the top-ranked 3 features re.select_feature_by_rank!('<=3') # number of features after feature selection puts ' # features (after): ' + re.get_features.size.to_s
3. feature selection after discretization
require 'fselector' # the Information Gain (IG) algorithm requires data with discrete feature r = ::.new # but the Iris data set contains continuous features r.data_from_url('http://repository.seasr.org/Datasets/UCI/arff/iris.arff', :weka) # let's first discretize it by ChiMerge algorithm at alpha=0.10 # then perform feature selection as usual r.discretize_by_ChiMerge!(0.10) # number of features before feature selection puts ' # features (before): ' + r.get_features.size.to_s # select the top-ranked feature r.select_feature_by_rank!('<=1') # number of features after feature selection puts ' # features (after): ' + r.get_features.size.to_s
4. see more examples test_*.rb under the test/ directory
How to contribute
check HowToContribute to see how to write your own feature selection algorithms and/or make contribution to FSelector.
A ChangeLog is available from version 0.5.0 and upward to refelect what's new and what's changed.