Returns the sum of a list, after mapping each element to a number using the provided function.
Use Iterable.map()
to map each element to the numeric value returned by fn
, Iterable.reduce()
to sum the values.
代码实现
num sumBy<T>(List<T> lst, num Function(T) fn) {
return lst.map(fn).reduce((num a, num b) => a + b);
}
使用样例
sumBy([ {'n': 4}, {'n': 2}, {'n': 8}, {'n': 6} ], (o) => o['n']); // 20