Groovy Goodness: Use Range by Method to Set Steps between Numbers

Groovy has support for defining ranges in the language. When we define a range of numbers, the steps between the values in the range is 1 by default. We can change the step size using the step method. This method accepts a int value with a new step size. The result is a List object with the values. Since Groovy 2.5.0 the by method is added to ranges with numbers. The by method accepts also decimal numbers and the result of the method is a NumberRange object instead of a List.

In the following example Groovy script, we first define a range with int values. We use the by method to change the step size using both an int value and BigDecimal value. We also use the by method for a range of BigDecimal numbers:

// Define range with int values.
def ints = 1..10

assert ints.from == 1
assert ints.to == 10
assert ints == [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
assert ints.class.name == 'groovy.lang.IntRange'

// Use by method to set steps
// between int values in range.
// The results is a new range.
def intsBy = ints.by(3)

assert intsBy.from == 1
assert intsBy.to == 10
assert intsBy == [1, 4, 7, 10]
assert intsBy.class.name == 'groovy.lang.NumberRange'

// Use step method to set steps
// between int values in range.
// The range is now converted to a List.
def intsStep = ints.step(3)

assert intsStep == [1, 4, 7, 10]
assert intsStep.class.name == 'java.util.ArrayList'

// Use by method to set step size to 0.9.
def intsBy2 = ints.by(0.9)

assert intsBy2.from == 1
assert intsBy2.to == 10
assert intsBy2 == [1, 1.9, 2.8, 3.7, 4.6, 5.5, 6.4, 7.3, 8.2, 9.1, 10.0]
assert intsBy2.class.name == 'groovy.lang.NumberRange'


// Define range with BigDecimal numbers.
def numbers = 1.0..4.5

assert numbers.from == 1.0
assert numbers.to == 4.5
assert numbers == [1.0, 2.0, 3.0, 4.0]
assert numbers.class.name == 'groovy.lang.NumberRange'

// Use by method to set step size
// between numbers to 0.5.
def numbersBy = numbers.by(0.5)

assert numbersBy.from == 1.0
assert numbersBy.to == 4.5
assert numbersBy == [1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5]
assert numbersBy.class.name == 'groovy.lang.NumberRange'

// We cannot use the step method to set
// step size to 0.5,
// because the step method only accepts
// int values as argument.
try {
    numbers.step(0.5)
} catch (MissingMethodException e) {
    assert e.message.contains('Possible solutions: step(int), step(int, groovy.lang.Closure)')
}

Written with Groovy 2.5.0.