Multiply each element of a list by an entire other list-CodePudding

I have two lists which are very large. The basic structure is : a = [1,0,0,0,1,1,0,0] and b=[1,0,1,0]. There is no restriction on the length of either list and there is also no restriction on the value of the elements in either list. I want to multiply each element of a by the contents of b. For example, the following code does the job:

multiplied = []
for a_bit in a:
     for b_bit in b:
          multiplied.append(a_bit*b_bit)

So for the even simpler case of a=[1,0] and b = [1,0,1,0], the output multiplied would be equal to:

>>> print(multiplied)
[1,0,1,0,0,0,0,0]

Is there a way with numpy or map or zip to do this? There are similar questions that are multiplying lists with lists and a bunch of other variations but I haven't seen this one. The problem is that, my nested for loops above are fine and they work but they take forever to process on larger arrays.

CodePudding user response：

You can do this using matrix multiplication, and then flattening the result.

>>> a = np.array([1,0]).reshape(-1,1)
>>> b = np.array([1,0,1,0])
>>> a*b
array([[1, 0, 1, 0],
       [0, 0, 0, 0]])
>>> (a*b).flatten()
array([1, 0, 1, 0, 0, 0, 0, 0])
>>>