how to sum a list

[echoeslove]

I want to use sum & divide, but the result is always 0

        List<Double> arr = Arrays.asList(1D, 2D, 3D, 4D);
        Double n = 2D;
        Expression expression = new Expression("sum(arr) / n");
        expression.with("arr", arr);
        expression.with("n", n);
        double val = expression.evaluate().getNumberValue().doubleValue();
        System.out.println("Result: " + val);

So that, I change the array values, code like this

        Double n = 2D;
        Expression expression = new Expression("sum(1,2,3,4) / n");
        expression.with("n", n);
        double val = expression.evaluate().getNumberValue().doubleValue();
        System.out.println("Result: " + val);

the result is correct

How to set the array value ?

[uklimaschewski]

Hi,

as of now, the sum(...) function does not support arrays as parameters.
I was planning to support arithmetic operations on arrays in general, but it is not implemented, yet.

If you want to contribute that special sum(...) functionality, fell free to to open a pull request.
It would be needed then to also have the min(...) and max(...) function to support arrays.

[uklimaschewski]

I have added this functionality in pull request #449:
The SUM, MIN and MAX functions now also can handle ARRAY parameter types. This also works for nested arrays and combinations of arrays and numbers.

It is already merged and will be released with version 3.2.0.

Here are some examples from the unit test:

  @Test
  void testSumSingleArray() throws EvaluationException, ParseException {
    Integer[] numbers = {1, 2, 3};

    Expression expression = new Expression("SUM(numbers)").with("numbers", numbers);

    assertThat(expression.evaluate().getStringValue()).isEqualTo("6");
  }

  @Test
  void testSumMultipleArray() throws EvaluationException, ParseException {
    Integer[] numbers1 = {1, 2, 3};
    Integer[] numbers2 = {4, 5, 6};

    Expression expression =
        new Expression("SUM(numbers1, numbers2)")
            .with("numbers1", numbers1)
            .with("numbers2", numbers2);

    assertThat(expression.evaluate().getStringValue()).isEqualTo("21");
  }

  @Test
  void testSumMixedArrayNumber() throws EvaluationException, ParseException {
    Integer[] numbers = {1, 2, 3};

    Expression expression = new Expression("SUM(numbers, 4)").with("numbers", numbers);

    assertThat(expression.evaluate().getStringValue()).isEqualTo("10");
  }

  @Test
  void testSumNestedArray() throws EvaluationException, ParseException {
    Integer[][] numbers = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};

    Expression expression = new Expression("SUM(numbers)").with("numbers", numbers);
    assertThat(expression.evaluate().getStringValue()).isEqualTo("45");
  }