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| <?php | |
| namespace CirrusSearch\Search\Rescore; | |
| use CirrusSearch\SearchConfig; | |
| use Elastica\Query\FunctionScore; | |
| /** | |
| * Utility function to compute a weighted geometric mean. | |
| * According to https://en.wikipedia.org/wiki/Weighted_geometric_mean | |
| * this is equivalent to exp ( w1*ln(value1)+w2*ln(value2) / (w1 + w2) ) ^ impact | |
| * impact is applied as a power factor because this function is applied in a | |
| * multiplication. | |
| * Members can use only LogScaleBoostFunctionScoreBuilder or SatuFunctionScoreBuilder | |
| * these are the only functions that normalize the value in the [0,1] range. | |
| */ | |
| class GeoMeanFunctionScoreBuilder extends FunctionScoreBuilder { | |
| /** @var float */ | |
| private $impact; | |
| /** @var array[] */ | |
| private $scriptFunctions = []; | |
| /** @var float */ | |
| private $epsilon = 0.0000001; | |
| /** | |
| * @param SearchConfig $config | |
| * @param float $weight | |
| * @param array $profile | |
| * @throws InvalidRescoreProfileException | |
| */ | |
| public function __construct( SearchConfig $config, $weight, $profile ) { | |
| parent::__construct( $config, $weight ); | |
| if ( isset( $profile['impact'] ) ) { | |
| $this->impact = $this->getOverriddenFactor( $profile['impact'] ); | |
| if ( $this->impact <= 0 ) { | |
| throw new InvalidRescoreProfileException( 'Param impact must be > 0' ); | |
| } | |
| } else { | |
| throw new InvalidRescoreProfileException( 'Param impact is mandatory' ); | |
| } | |
| if ( isset( $profile['epsilon'] ) ) { | |
| $this->epsilon = $this->getOverriddenFactor( $profile['epsilon'] ); | |
| } | |
| if ( !isset( $profile['members'] ) || !is_array( $profile['members'] ) ) { | |
| throw new InvalidRescoreProfileException( 'members must be an array of arrays' ); | |
| } | |
| foreach ( $profile['members'] as $member ) { | |
| if ( !is_array( $member ) ) { | |
| throw new InvalidRescoreProfileException( "members must be an array of arrays" ); | |
| } | |
| if ( !isset( $member['weight'] ) ) { | |
| $weight = 1; | |
| } else { | |
| $weight = $this->getOverriddenFactor( $member['weight'] ); | |
| } | |
| $function = [ 'weight' => $weight ]; | |
| switch ( $member['type'] ) { | |
| case 'satu': | |
| $function['script'] = | |
| new SatuFunctionScoreBuilder( $this->config, 1, | |
| $member['params'] ); | |
| break; | |
| case 'logscale_boost': | |
| $function['script'] = | |
| new LogScaleBoostFunctionScoreBuilder( $this->config, 1, | |
| $member['params'] ); | |
| break; | |
| default: | |
| throw new InvalidRescoreProfileException( "Unsupported function in {$member['type']}." ); | |
| } | |
| $this->scriptFunctions[] = $function; | |
| } | |
| if ( count( $this->scriptFunctions ) < 2 ) { | |
| throw new InvalidRescoreProfileException( "At least 2 members are needed to compute a geometric mean." ); | |
| } | |
| } | |
| /** | |
| * Build a weighted geometric mean using a logarithmic arithmetic mean. | |
| * exp(w1*ln(value1)+w2*ln(value2) / (w1+w2)) | |
| * NOTE: We need to use an epsilon value in case value is 0. | |
| * | |
| * @return string|null the script | |
| */ | |
| public function getScript() { | |
| $formula = "pow("; | |
| $formula .= "exp(("; | |
| $first = true; | |
| $sumWeight = 0; | |
| foreach ( $this->scriptFunctions as $func ) { | |
| if ( $first ) { | |
| $first = false; | |
| } else { | |
| $formula .= " + "; | |
| } | |
| $sumWeight += $func['weight']; | |
| $formula .= "{$func['weight']}*ln(max("; | |
| $formula .= $func['script']->getScript(); | |
| $formula .= ", {$this->epsilon}))"; | |
| } | |
| if ( $sumWeight == 0 ) { | |
| return null; | |
| } | |
| $formula .= ")"; | |
| $formula .= "/ $sumWeight )"; | |
| $formula .= ", {$this->impact})"; // pow( | |
| return $formula; | |
| } | |
| public function append( FunctionScore $functionScore ) { | |
| $formula = $this->getScript(); | |
| if ( $formula != null ) { | |
| $functionScore->addScriptScoreFunction( new \Elastica\Script\Script( $formula, null, | |
| 'expression' ), null, $this->weight ); | |
| } | |
| } | |
| } |