【Numpy】Numpy均值计算的七七八八-条件-行列

写Numpy均值的文章挺多的，就是花式用法不够全，总结一下

Numpy均值计算方法

有两种

1. numpy.mean(a, axis=None, dtype=None, out=None, keepdims=, *, where=)
2. numpy.average(a, axis=None, weights=None, returned=False, *, keepdims=)
   两者的区别在于是否能计算加权平均

Numpy.mean

不带权重的均值

axis

>>> a = np.array([[1, 2], [3, 4]])
>>> np.mean(a)
2.5
>>> np.mean(a, axis=0)
array([2., 3.])
>>> np.mean(a, axis=1)
array([1.5, 3.5])
>>> np.mean(a[