Implementations for built-in STDEV in Virtuoso, Fuseki, Stardog, Sesame

sd-builtin-fuseki.sparql

PREFIX bsbm:  <http://www4.wiwiss.fu-berlin.de/bizer/bsbm/v01/vocabulary/> 
PREFIX bsbmi: <http://www4.wiwiss.fu-berlin.de/bizer/bsbm/v01/instances/> 
PREFIX afn: <http://jena.hpl.hp.com/ARQ/function#> 

SELECT ?vendor 
       (COUNT(?review) AS ?count) 
       (AVG(?rating) AS ?mean) 
       (afn:sqrt( ( ( sum(?rating*?rating)-sum(?rating)*sum(?rating)/count(?rating) ) / (count(?rating)-1) ) ) AS ?stdev) 
WHERE { 
    GRAPH <http://scry.rocks/bsbm1> {
      ?review bsbm:reviewFor ?product ; 
      bsbm:rating1   ?rating . 
      ?offer bsbm:product ?product ; 
      bsbm:vendor ?vendor . 
    }
} GROUP BY ?vendor

sd-builtin-sesame.sparql

PREFIX bsbm:  <http://www4.wiwiss.fu-berlin.de/bizer/bsbm/v01/vocabulary/>
PREFIX bsbmi: <http://www4.wiwiss.fu-berlin.de/bizer/bsbm/v01/instances/>
PREFIX func: <http://example.org/custom-function/>

SELECT ?vendor ?count ?mean ?stdev WHERE {
  {
SELECT  ?vendor
       (COUNT(?review) AS ?count)
       (AVG(?rating) AS ?mean)
    (( ( sum(?rating*?rating)-sum(?rating)*sum(?rating)/count(?rating) ) / (count(?rating)-1) )  AS ?var)
WHERE {
  ?review bsbm:reviewFor ?product ;
  				bsbm:rating1   ?rating .
  		?offer bsbm:product ?product ;
    		   bsbm:vendor ?vendor .
  } GROUP BY ?vendor
}
  bind (func:sqrt(?var) as ?stdev)
}

sd-builtin-stardog.sparql

PREFIX bsbm:  <http://www4.wiwiss.fu-berlin.de/bizer/bsbm/v01/vocabulary/>
PREFIX bsbmi: <http://www4.wiwiss.fu-berlin.de/bizer/bsbm/v01/instances/>
PREFIX math: <http://www.w3.org/2005/xpath-functions/math#>

SELECT ?vendor
       (COUNT(?review) AS ?count)
       (AVG(?rating) AS ?mean)
       (math:sqrt( ( ( sum(?rating*?rating)-sum(?rating)*sum(?rating)/count(?rating) ) / (count(?rating)-1) ) ) AS ?stdev) 
WHERE {
    ?review bsbm:reviewFor ?product ;
  				bsbm:rating1   ?rating .
  		?offer bsbm:product ?product ;
    		   bsbm:vendor ?vendor .
} GROUP BY ?vendor

sd-builtin-virtuoso.sparql

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX bsbm:  <http://www4.wiwiss.fu-berlin.de/bizer/bsbm/v01/vocabulary/>
PREFIX bsbmi: <http://www4.wiwiss.fu-berlin.de/bizer/bsbm/v01/instances/>
SELECT ?vendor
       (COUNT(?review) AS ?count)
       (AVG(?rating) AS ?mean)
       (sql:STDDEV(?rating) as ?sd) 
WHERE {
  GRAPH <http://scry.rocks/bsbm1> {
    ?review bsbm:reviewFor ?product ;
  				bsbm:rating1   ?rating .
  		?offer bsbm:product ?product ;
    		   bsbm:vendor ?vendor .
  } 
} GROUP BY ?vendor

sesame-sqrt.java

package org.example.customfunction;
import org.openrdf.query.algebra.evaluation.function.Function;
import org.openrdf.query.algebra.evaluation.ValueExprEvaluationException;
import org.openrdf.model.impl.*;
import org.openrdf.model.*;
import java.lang.*;
/**
* a custom SPARQL function that determines whether an input literal string is
* a palindrome.
*/
public class SqrtFunc implements Function {
// define a constant for the namespace of our custom function
public static final String NAMESPACE = "http://example.org/custom-function/";
/**
* return the URI 'http://example.org/custom-function/palindrome' as a String
*/
public String getURI() {
return NAMESPACE + "sqrt";
}
/**
* Executes the sqrt function.
*
* @return A double with the sqrt() of the parameter
*
* @throws ValueExprEvaluationException
* if more than one argument is supplied or if the supplied argument is
* not a literal.
*/
public Value evaluate(ValueFactory valueFactory, Value... args)
throws ValueExprEvaluationException
{
// our sqrt function expects only a single argument, so throw an error
// if there's more than one
if (args.length != 1) {
throw new ValueExprEvaluationException("sqrt function requires" +
"exactly 1 argument, got " + args.length);
}
Value arg = args[0];
// check if the argument is a double, if not, we throw an error
if (! (arg instanceof Literal)) {
throw new ValueExprEvaluationException(
"invalid argument (literal expected): " + arg);
}
else {
// get the integer value that we want to calculate its sqrt
double num = Double.parseDouble(((Literal)arg).getLabel());

// the resulting sqrt
double sqrt = Math.sqrt(num);
// a function is always expected to return a Value object, so we
// return our boolean result as a Literal
return valueFactory.createLiteral(sqrt);
}
}
}