poi/src/java/org/apache/poi/ss/formula/functions/Delta.java

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   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
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package org.apache.poi.ss.formula.functions;

import org.apache.poi.ss.formula.OperationEvaluationContext;
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.OperandResolver;
import org.apache.poi.ss.formula.eval.ValueEval;

/**
 * Implementation for Excel DELTA() function.<p>
 * <p>
 * <b>Syntax</b>:<br> <b>DELTA </b>(<b>number1</b>,<b>number2</b> )<br>
 * <p>
 * Tests whether two values are equal. Returns 1 if number1 = number2; returns 0 otherwise.
 * Use this function to filter a set of values. For example, by summing several DELTA functions
 * you calculate the count of equal pairs. This function is also known as the Kronecker Delta function.
 *
 * <ul>
 *     <li>If number1 is nonnumeric, DELTA returns the #VALUE! error value.</li>
 *     <li>If number2 is nonnumeric, DELTA returns the #VALUE! error value.</li>
 * </ul>
 *
 * @author cedric dot walter @ gmail dot com
 */
public final class Delta extends Fixed2ArgFunction implements FreeRefFunction {

    public static final FreeRefFunction instance = new Delta();

    private static final NumberEval ONE = new NumberEval(1);
    private static final NumberEval ZERO = new NumberEval(0);

    public ValueEval evaluate(int srcRowIndex, int srcColumnIndex, ValueEval arg1, ValueEval arg2) {
        try {
            Double number1 = evaluateValue(arg1, srcRowIndex, srcColumnIndex);
            if (number1 == null) {
                return ErrorEval.VALUE_INVALID;
            }
            Double number2 = evaluateValue(arg2, srcRowIndex, srcColumnIndex);
            if (number2 == null) {
                return ErrorEval.VALUE_INVALID;
            }

            return (number1.compareTo(number2) == 0) ? ONE : ZERO;
        } catch (EvaluationException e) {
            return e.getErrorEval();
        }
    }

    public ValueEval evaluate(ValueEval[] args, OperationEvaluationContext ec) {
         if (args.length == 2) {
            return evaluate(ec.getRowIndex(), ec.getColumnIndex(), args[0], args[1]);
        }

        return ErrorEval.VALUE_INVALID;
    }

    private static Double evaluateValue(ValueEval arg, int srcRowIndex, int srcColumnIndex) throws EvaluationException {
        ValueEval veText = OperandResolver.getSingleValue(arg, srcRowIndex, srcColumnIndex);
        String strText1 = OperandResolver.coerceValueToString(veText);
        return OperandResolver.parseDouble(strText1);
    }
}