numpy.round的奇怪行为 [英] Strange behavior of numpy.round

问题描述

面对x.5数字，Python的round()似乎总是四舍五入:

Python's round() seems to always round up when faced with x.5 numbers:

print round(1.5),round(2.5),round(3.5),round(4.5)
>>> 2.0 3.0 4.0 5.0

但是numpy.round()似乎不一致:

import numpy as np
print np.round(1.5),np.round(2.5),np.round(3.5),np.round(4.5)
>>> 2.0 2.0 4.0 4.0

在某些情况下，这可能会导致错误.这是错误还是我错过了什么?

This can introduce errors in certain cases. Is this a bug or am I missing something?

推荐答案

numpy舍入到最接近的偶数值:

numpy rounds to the nearest even value:

https://docs.scipy .org/doc/numpy/reference/generated/numpy.around.html#numpy.around

对于恰好位于四舍五入的十进制值中间的值，NumPy会四舍五入为最接近的偶数.因此1.5和2.5四舍五入为2.0，-0.5和0.5四舍五入为0.0，等等.

For values exactly halfway between rounded decimal values, NumPy rounds to the nearest even value. Thus 1.5 and 2.5 round to 2.0, -0.5 and 0.5 round to 0.0, etc.

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