Correl.java

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package org.apache.poi.ss.formula.functions;

import org.apache.commons.math3.stat.correlation.PearsonsCorrelation;
import org.apache.poi.ss.formula.eval.ErrorEval;
import org.apache.poi.ss.formula.eval.EvaluationException;
import org.apache.poi.ss.formula.eval.NumberEval;
import org.apache.poi.ss.formula.eval.ValueEval;

import java.util.List;

import static org.apache.poi.ss.formula.functions.ArrayFunctionUtils.getNumberArrays;

/**
 * Implementation for Excel CORREL() function.
 * <p>
 *   <b>Syntax</b>:<br> <b>CORREL </b>(<b>array1</b>, <b>array2</b>)<br>
 * </p>
 * <p>
 *   The CORREL function returns the correlation coefficient of two cell ranges.
 *   Use the correlation coefficient to determine the relationship between two properties.
 *   For example, you can examine the relationship between a location's average temperature and the use of air conditioners.
 * </p>
 * <p>
 *   See https://support.microsoft.com/en-us/office/correl-function-995dcef7-0c0a-4bed-a3fb-239d7b68ca92
 * </p>
 */
public class Correl extends Fixed2ArgFunction {

    public static final Correl instance = new Correl();

    private Correl() {}

    @Override
    public ValueEval evaluate(int srcRowIndex, int srcColumnIndex, ValueEval arg0, ValueEval arg1) {
        try {
            final List<DoubleList> arrays = getNumberArrays(arg0, arg1);
            final PearsonsCorrelation pc = new PearsonsCorrelation();
            final double correl = pc.correlation(
                    arrays.get(0).toArray(), arrays.get(1).toArray());
            return new NumberEval(correl);
        } catch (EvaluationException e) {
            return e.getErrorEval();
        } catch (Exception e) {
            return ErrorEval.NA;
        }
    }
}