Merge two arrays from a given index - PYTHON

Question

I am wondering if there is an easy way to 'append' new elements to an array, but not at the end

Imagine I have a vector

a = np.array([1,2,3,4,5,6])

I want to append a new vector

b = np.array([1,1,1,1])

to a, starting from element 3 so that the new array would be

c = np.array([1,2,3,5,6,7,1])

that is the last 3 elements of array a are resulting from a+b while the new element just belong to C

Any ideas?

THX

I tried just append!

"that is the last 3 elements of array a are resulting from a+b while the new element just belong to C" What you are describing isn't really an "append" operation. — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Nov 7, 2022 at 19:48
@user Please clarify the logic behind what you're trying to do. What's the connection between the arrays you start with ([1,2,3,4,5,6] and [1,1,1,1]) and the array you end up with [1,2,3,5,6,7,1]? My best guess at the logic here is that you want to find [1,2,3,4+1,5+1,6+1,0+1]. Is that right? — Ben Grossmann
– Ben Grossmann, Commented Nov 7, 2022 at 19:54

mozway · Accepted Answer · 2022-11-07 19:51:48Z

2

Using numpy with pad:

a = np.array([1,2,3,4,5,6])
b = np.array([1,1,1,1])
# or
# a = [1,2,3,4,5,6]
# b = [1,1,1,1]

n = 3
extra = len(b)-len(a)+n

c = np.pad(a, (0, extra))
c[n:] += b

Output:

array([1, 2, 3, 5, 6, 7, 1])

answered Nov 7, 2022 at 19:51

mozway

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Ben Grossmann Over a year ago

OP has since clarified that the question is indeed about numpy arrays

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