python - 带有 numpy 数组的 numpy 日志

Question

我想了解为什么会出现以下代码:

print((hypothesis(x, theta_)))

以这种格式生成一个数组

[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]

为什么我应用log函数时，数组的格式不一样？

Answer 1

大概 hypothesis(x, theta_) 返回一个 python list。打印列表时，会包含逗号。

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 不在打印输出中包含逗号？这是你必须问 numpy 开发人员的事情。它确实使输出不那么困惑，但如果您想将打印的值复制并粘贴回其他代码，这可能会很麻烦。

如果您打印“repr”，则输出包含名称 array，并且包含逗号:

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