Numpy [...，无](Numpy […,None])

 我发现自己需要为现有的numpy数组添加功能，这导致了下面代码的最后部分实际上在做什么的问题： 
 
   np.ones(shape=feature_set.shape)[...,None]
 
 建立 
 
 举个例子，假设我希望通过使用numpy和求解来求解线性回归参数估计： 
 
  
 
 假设我有一个特征集形状（50,1），一个形状的目标变量（50，），我希望使用我的目标变量的形状来为拦截值添加一列。 
 
 它看起来像这样： 
 
# Create random target & feature set
y_train = np.random.randint(0,100, size = (50,))
feature_set = np.random.randint(0,100,size=(50,1))

# Build a set of 1s after shape of target variable
int_train = np.ones(shape=y_train.shape)[...,None]

# Able to then add int_train to feature set 
X = np.concatenate((int_train, feature_set),1)
 
 我认为我知道的 
 
 当我将[...，None]与我离开时相比时，我看到输出的差异。 这里是： 
 
  
 
 第二个版本在需要相同维数的输入数组周围返回错误，最终我偶然发现使用[...，None]的解决方案。 
 
 主要问题 
 
 虽然我看到[...，None]的输出给了我想要的东西，但我很难找到关于它实际上应该做什么的任何信息。 任何人都可以告诉我这个代码实际意味着什么， None参数是做什么的，等等？ 
 
 谢谢！ 

I have found myself needing to add features to existing numpy arrays which has led to a question around what the last portion of the following code is actually doing: 
 
   np.ones(shape=feature_set.shape)[...,None]
 
Set-up
 
As an example, let's say I wish to solve for linear regression parameter estimates by using numpy and solving: 
 
 
Assume I have a feature set shape (50,1), a target variable of shape (50,), and I wish to use the shape of my target variable to add a column for intercept values.
 
It would look something like this: 
 
# Create random target & feature set
y_train = np.random.randint(0,100, size = (50,))
feature_set = np.random.randint(0,100,size=(50,1))

# Build a set of 1s after shape of target variable
int_train = np.ones(shape=y_train.shape)[...,None]

# Able to then add int_train to feature set 
X = np.concatenate((int_train, feature_set),1)
 
What I Think I Know
 
I see the difference in output when I include [...,None] vs when I leave it off. Here it is: 
 
 
The second version returns an error around input arrays needing the same number of dimensions, and eventually I stumbled on the solution to use [...,None].
 
Main Question
 
While I see the output of [...,None] gives me what I want, I am struggling to find any information on what it is actually supposed to do. Can anybody walk me through what this code actually means, what the None argument is doing, etc? 
 
Thank you!

原文：https://stackoverflow.com/questions/51127657