CODEWITHSUNDEEP
pythonarraysnumpy
Jay
Jay

Reputation: 291

Remove elements from the array

I have two arrays, that I am trying to combine using concatenate:

a = np.array(([1,2], [5,6], [9,10]))
b = np.array(([3,4], [7,8], [11,12], [13,14], [17,18]))
c = np.concatenate((a,b), 1)

This wont work because the lengths of the arrays are different. Therefore I am using len to compare the lengths of the two arrays and then determine the length for c based on the minimum length:

alength = len(a)
blength = len(b)
lengthforc = min(alength, blength)

In this example the minimum lengthforc is 3. Therefore I am trying an if statement to reduce the length of b by deleting the last two rows(elements).

if blength > lengthforc:
   rowstoremove = blength - lengthforc

How can I modify this if statement to carry out what I want (as the number of rows to remove will change), unless there is another way?. The final array should be:

>>> print c
  [[ 1  2  3  4]
  [ 5  6  7  8]
  [ 9 10 11 12]]

Upvotes: 1

Views: 157

Answers (2)

Mike Müller
Mike Müller

Reputation: 85442

Try hstack:

a = np.array(([1,2], [5,6], [9,10]))
b = np.array(([3,4], [7,8], [11,12], [13,14], [17,18]))
end = min(a.shape[0], b.shape[0])
np.hstack((a[:end], b[:end]))

Result:

array([[ 1,  2,  3,  4],
       [ 5,  6,  7,  8],
       [ 9, 10, 11, 12]])

EDIT

If you don't need NumPy arrays you can go with lists:

a_list = [[1,2], [5,6], [9,10]]
b_list = [[3,4], [7,8], [11,12], [13,14], [17,18]]

Just one line:

[x + y for x, y in zip(a_list, b_list)]

Result:

[[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]

Upvotes: 1

storaged
storaged

Reputation: 1847

I'm not sure if I got the problem correctly (in my solution I just used lists), but is it just that simple ? 

a = [[1,2], [5,6], [9,10]]
b = [[3,4], [7,8], [11,12], [13,14], [17,18]]
c = []
for x,y in zip(a,b):
    c.append(x+y)

Upvotes: 0

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