[BAEL-3489] Added Java-R integration examples.

libraries-data-2/src/main/java/com/baeldung/r/FastRMean.java

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+package com.baeldung.r;
+
+import java.io.IOException;
+import java.net.URISyntaxException;
+
+/**
+ * FastR showcase.
+ * 
+ * @author Donato Rimenti
+ */
+public class FastRMean {
+
+	/**
+	 * Invokes the customMean R function passing the given values as arguments.
+	 * 
+	 * @param values the input to the mean script
+	 * @return the result of the R script
+	 */
+	public double mean(int[] values) {
+		Context polyglot = Context.newBuilder().allowAllAccess(true).build();
+		String meanScriptContent = RUtils.getMeanScriptContent();
+		polyglot.eval("R", meanScriptContent);
+		Value rBindings = polyglot.getBindings("R");
+		Value rInput = rBindings.getMember("c").execute(values);
+		return rBindings.getMember("customMean").execute(rInput).asDouble();
+	}
+
+}

libraries-data-2/src/main/java/com/baeldung/r/RCallerMean.java

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+package com.baeldung.r;
+
+import java.io.IOException;
+import java.net.URISyntaxException;
+
+import com.github.rcaller.rstuff.RCaller;
+import com.github.rcaller.rstuff.RCallerOptions;
+import com.github.rcaller.rstuff.RCode;
+
+/**
+ * RCaller showcase.
+ * 
+ * @author Donato Rimenti
+ */
+public class RCallerMean {
+
+	/**
+	 * Invokes the customMean R function passing the given values as arguments.
+	 * 
+	 * @param values the input to the mean script
+	 * @return the result of the R script
+	 * @throws IOException        if any error occurs
+	 * @throws URISyntaxException if any error occurs
+	 */
+	public double mean(int[] values) throws IOException, URISyntaxException {
+		String fileContent = RUtils.getMeanScriptContent();
+		RCode code = RCode.create();
+		code.addRCode(fileContent);
+		code.addIntArray("input", values);
+		code.addRCode("result <- customMean(input)");
+		RCaller caller = RCaller.create(code, RCallerOptions.create());
+		caller.runAndReturnResult("result");
+		return caller.getParser().getAsDoubleArray("result")[0];
+	}
+
+}

libraries-data-2/src/main/java/com/baeldung/r/RUtils.java

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+package com.baeldung.r;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.stream.Collectors;
+
+/**
+ * Utility class for loading the script.R content.
+ * 
+ * @author Donato Rimenti
+ */
+public class RUtils {
+
+	/**
+	 * Loads the script.R and returns its content as a string.
+	 * 
+	 * @return the script.R content as a string
+	 * @throws IOException        if any error occurs
+	 * @throws URISyntaxException if any error occurs
+	 */
+	static String getMeanScriptContent() throws IOException, URISyntaxException {
+		URI rScriptUri = RUtils.class.getClassLoader().getResource("script.R").toURI();
+		Path inputScript = Paths.get(rScriptUri);
+		return Files.lines(inputScript).collect(Collectors.joining());
+	}
+}

libraries-data-2/src/main/java/com/baeldung/r/RenjinMean.java

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+package com.baeldung.r;
+
+import java.io.IOException;
+import java.net.URISyntaxException;
+
+import javax.script.ScriptException;
+
+import org.renjin.script.RenjinScriptEngine;
+import org.renjin.sexp.DoubleArrayVector;
+
+/**
+ * Renjin showcase.
+ * 
+ * @author Donato Rimenti
+ */
+public class RenjinMean {
+
+	/**
+	 * Invokes the customMean R function passing the given values as arguments.
+	 * 
+	 * @param values the input to the mean script
+	 * @return the result of the R script
+	 * @throws IOException        if any error occurs
+	 * @throws URISyntaxException if any error occurs
+	 * @throws ScriptException    if any error occurs
+	 */
+	public double mean(int[] values) throws IOException, URISyntaxException, ScriptException {
+		RenjinScriptEngine engine = new RenjinScriptEngine();
+		String meanScriptContent = RUtils.getMeanScriptContent();
+		engine.put("input", values);
+		engine.eval(meanScriptContent);
+		DoubleArrayVector result = (DoubleArrayVector) engine.eval("customMean(input)");
+		return result.asReal();
+	}
+
+}

libraries-data-2/src/main/java/com/baeldung/r/RserveMean.java

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+package com.baeldung.r;
+
+import org.rosuda.REngine.REXPMismatchException;
+import org.rosuda.REngine.REngineException;
+import org.rosuda.REngine.Rserve.RConnection;
+
+/**
+ * Rserve showcase.
+ * 
+ * @author Donato Rimenti
+ */
+public class RserveMean {
+
+	/**
+	 * Connects to the Rserve istance listening on 127.0.0.1:6311 and invokes the
+	 * customMean R function passing the given values as arguments.
+	 * 
+	 * @param values the input to the mean script
+	 * @return the result of the R script
+	 * @throws REngineException      if any error occurs
+	 * @throws REXPMismatchException if any error occurs
+	 */
+	public double mean(int[] values) throws REngineException, REXPMismatchException {
+		RConnection c = new RConnection();
+		c.assign("input", values);
+		return c.eval("customMean(input)").asDouble();
+	}
+
+}