sumByDouble method
Returns the sum of all values produced by the selector
function that is
applied to each element.
Example:
[1.5, 2.5].sumByDouble((d) => 0.5 * d); // 2.0
Implementation
double sumByDouble(num Function(T) selector) {
ArgumentError.checkNotNull(selector, 'selector');
return map(selector).fold(0.0, (prev, curr) => prev + curr);
}