OrdinalScale<D, R> constructor
Creates an ordinal scale with the given parameters.
Implementation
OrdinalScale({
List<D>? domain,
List<R>? range,
R? unknown,
}) : _unknown = unknown {
// Range must be set before domain because domain setter calls _getRange
if (range != null) this.range = range;
if (domain != null) this.domain = domain;
}