Append an array to another array

Question

I have a problem with `np.append(ar,values, axis=None)`

Take a look at following codes:

import numpy as np

array1 = np.array([])
array2 = np.array([1,2])
array3 = np.array([3,4])
array4 = np.array([5,6])

array1 = np.append(array1, array2)
array1 = np.append(array1, array3)
array1 = np.append(array1, array4)

print(array1) # [1. 2. 3. 4. 5. 6.]

So this is not what i want i want add exactly the array to the array1 and the array1 should be

[[1. 2.]
 [3. 4.]
 [5. 6.]]

How can i do that?

don't use np.append - unless you want to add just one number to a 1d array. — hpaulj
– hpaulj, Commented Feb 12, 2022 at 14:23

score 1 · Accepted Answer · 2022-02-12 10:30:43Z

1

You need to stack the arrays.

array1 = np.stack([array2, array3, array4])

should do it.

edited Feb 12, 2022 at 10:30

answered Feb 12, 2022 at 10:19

user6954761

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2 Comments

amirhossein zibaei Over a year ago

ValueError: all input arrays must have the same shape

user6954761 Over a year ago

Corrected the answer, stack takes a list (or array like) of other arrays that you want to stack vertically.

Rohith Nambiar · Accepted Answer · 2022-02-12 10:43:21Z

0

Try this:

import numpy as np

array1 = np.array([])
array2 = np.array([1,2])
array3 = np.array([3,4])
array4 = np.array([5,6])
a = np.append(array1, array2)
b = np.append(array1, array3)
c = np.append(array1, array4)
print(np.vstack((a, b, c)))

output:

[[1. 2.]
 [3. 4.]
 [5. 6.]]

edited Feb 12, 2022 at 10:43

answered Feb 12, 2022 at 10:37

Rohith Nambiar

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I have a problem with `np.append(ar,values, axis=None)`