arrays - Ruby:sum 与 inject(:+) 产生不同的结果

Question

我注意到 array.sum 和 array.inject(:+) 产生不同的结果。这是什么原因？

a = [10, 1.1, 6.16]

a.inject(:+)
# => 17.259999999999998

a.sum
# => 17.26

Answer 1

Array#sum 的 C 实现委托(delegate)给 Kahan summation algorithm当它的一些输入是 float 时。

这个算法...

...significantly reduces the numerical error in the total obtained by adding a sequence of finite precision floating point numbers, compared to the obvious approach. This is done by keeping a separate running compensation (a variable to accumulate small errors).

-- Wikipedia

参见 Array#sum和 implementation on Github .