具有numpy数组的numpy日志

Question

我想了解为什么下面的代码：

print((hypothesis(x, theta_)))

生成具有此格式的数组。

[0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5,
 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5,
 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 
 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 
 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5,
 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5,    
 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5]

当我应用numpy.log函数时：

print(np.log(hypothesis(x, theta_)))

我得到以下结果

[-0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718 -0.69314718
 -0.69314718 -0.69314718 -0.69314718 -0.69314718]

当我应用日志函数时，为什么数组的格式不同？

Answer 1

据推测，hypothesis(x, theta_)返回一个python列表。打印列表时，将包括逗号。

np.log(hypothesis(x, theta_))返回一个numpy数组。打印numpy数组时，不包括逗号。

例如：

In [1]: x = [1, 2, 3]  # `x` is a python list.

In [2]: print(x)
[1, 2, 3]

In [3]: a = np.array(x)  # `a` is a numpy array.

In [4]: print(a)
[1 2 3]

为什么numpy在打印输出中不包括逗号？这是你必须要问的那些不起眼的开发者。它确实减少了输出的杂乱，但如果您想要将打印的值复制并粘贴到其他代码中，则可能会带来麻烦。

如果打印"repr"，则输出包含名称array，并包含逗号：

In [6]: print(repr(a))
array([1, 2, 3])