# Get average between consecutive pairs of numpy array

## Question:

Say I have a numpy array like this

`[1,2,3,4,5]`

I want to generate an array that is the equal to the average of consecutive elements

`[1.5,2.5,3.5,4.5]`

Is there any efficient way to do this outside of just iterating through?

I’m not really sure what to do because reshaping doesn’t really work and I’m trying to get a smaller array.

## Answers:

Using NumPy’s vectorized operation (highly-optimized functions for performing mathematical operations) in the code below.

`arr[:-1]`

contains all but the last element of arr

`arr[1:]`

contains all but the first element of arr

```
import numpy as np
arr = np.array([1, 2, 3, 4, 5, 6, 7, 8])
avg_arr = (arr[:-1] + arr[1:]) / 2.0
print(avg_arr)
```

You can use `np.convolve`

to implement two-element averaging as the convolution of the input vector with the vector `[0.5, 0.5]`

:

```
>>> a = [1, 2, 3, 4, 5]
>>> np.convolve(a, [0.5, 0.5], "valid")
array([1.5, 2.5, 3.5, 4.5])
```

`np.convolve`

is a highly optimized routine, and will delegate to different implementations depending on what it estimates will be fastest for the given inputs. For small vectors like `[0.5, 0.5]`

it will likely just compute the result directly (`0.5*a[n] + 0.5*[n+1]`

for each element), but for large inputs it can leverage FFT-based convolution algorithms to compute the result with significantly fewer operations than the direct method.