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package Algorithm::ContextVector;
use strict;
use warnings;

our $VERSION = 0.01;

=head1 NAME

Algorithm::ContextVector - Simple implementation based on Data::CosineSimilarity

=head1 SYNOPSIS

 my $cv = Algorithm::ContextVector->new( top => 300 );

 $cs->add_instance( label => 'label1', attributes => { feature1 => 3, feature2 => 1, feature3 => 10 } );
 $cs->add_instance( label => [ 'label2', 'label3' ], attributes => { ... } );
 $cs->add_instance( label => ..., attributes => ... );
 ...

 $cv->train;

 my $results = $cv->predict( attributes => { ... } );

=head1 DESCRIPTION

Simple implementation based on Data::CosineSimilarity

=head2 $class->new( top => ... )

During the training, keeps the $top most heavy weighted features.
Keeps the complete feature set if omitted.

=cut

use Data::CosineSimilarity;
use Storable;

sub new {
    my $class = shift;
    my %opts = @_;
    return bless {
        top => $opts{top},
        labels => {},
    }, $class;
}

=head2 $class->new_from_file( $filename )

Returns the instance of Algorithm::ContextVector stored in $filename.

=cut

sub new_from_file {
    my $class = shift;
    my ($file) = @_;
    return retrieve($file);
}

=head2 $self->save_to_file( $filename )

Save the $self to $filename using Storable.

=cut

sub save_to_file {
    my $self = shift;
    my ($file) = @_;
    store($self, $file);
}

sub _add_hashrefs {
    my $self = shift;
    my @list = @_;
    my %r;
    for my $h (@list) {
        for my $key (keys %$h) {
            $r{$key} ||= 0;
            $r{$key} = $r{$key} + $h->{$key};
        }
    }
    return \%r;
}

=head2 $self->add_instance( label => [ ... ], attributes => { ... } )

=cut

sub add_instance {
    my $self = shift;
    my %args = @_;

    my $attr = $args{attributes} or die 'attributes required';
    return unless keys %$attr;

    my $labels = $args{label} or die 'label required';
    $labels = [ $labels ] unless ref $labels;

    for $_ (@$labels) {
        $self->{labels}{$_}{features} ||= {};
        $self->{labels}{$_}{features} = $self->_add_hashrefs(
            $self->{labels}{$_}{features}, $attr