I'm trying to speed up my code and right now I have a "for" loop to sum numbers in an array. It's set up like this:

a1=np.zeros(5)
a2=[1,2,3,4,5,6,7,8,9,10]

And what I want to do is sum the values of a2[:5] a2[5:], to end up with

a1=[7,9,11,13,15]

So I've made a loop that goes:

for ii in range(2):
    a1 =a2[5*ii:5*(ii 1)]

However, this is taking really long. Does anyone have any ideas on how to get around this or how to restructure my code?

I want to do:

i=np.range(2)
a1 =a2[5*i:5*(i 1)]

But can't, since you can't use arrays as indices in Python. That's the only other idea I've had besides the loop.

Edit: the 2 here is just an example, in my code I'm planning on having it do this like 50-100 times.

CodePudding user response：

It looks like you would like to add the first half of the list to its second half. This can be accomplished by reshaping the 1D list into a 2D array (2x5) and summing it along the horizontal axis.

np.array(a2).reshape(2,5).sum(axis=0)
# array([ 7,  9, 11, 13, 15])

CodePudding user response：

Depends on what you really want to achieve. but the np.roll function might get the speed you are looking for:

a2 = np.array([1,2,3,4,5,6,7,8,9,10])
a1 = a2[:5]   np.roll(a2, -5)[:5]