range function Ticks

List<num> range({ num start = 0, required num stop, num step = 1, })

Returns an list containing an arithmetic progression, similar to the Python built-in range.

This method is often used to iterate over a sequence of uniformly-spaced numeric values, such as the indexes of an list or the ticks of a linear scale. (See also ticks for nicely-rounded values.)

If step is omitted, it defaults to 1. If start is omitted, it defaults to 0. The stop value is exclusive; it is not included in the result. If step is positive, the last element is the largest start + i * step less than stop; if step is negative, the last element is the smallest start + i * step greater than stop. If the returned list would contain an infinite number of values, an empty range is returned.

The arguments are not required to be integers; however, the results are more predictable if they are. The values in the returned list are defined as start + i * step, where i is an integer from zero to one minus the total number of elements in the returned list. For example:

range(start: 0, stop: 1, step: 0.2); // [0, 0.2, 0.4, 0.6000000000000001, 0.8]

This unexpected behavior is due to IEEE 754 double-precision floating point, which defines 0.2 * 3 = 0.6000000000000001. Use d4_format to format numbers for human consumption with appropriate rounding; see also linear.tickFormat in d4_scale.

Likewise, if the returned list should have a specific length, consider using List.map on an integer range. For example:

range(start: 0, stop: 1, step: 1 / 49); // BAD: returns 50 elements!
range(stop: 49).map((d) => d / 49); // GOOD: returns 49 elements.

Implementation

List<num> range({num start = 0, required num stop, num step = 1}) {
  var n = ((stop - start) / step).ceilToDouble();

  if (!n.isFinite || n.isNegative) n = 0;

  return List.generate(n.truncate(), (i) => (start + i * step));
}