Appending numpy array of arrays

Question

I am trying to append an array to another array but its appending them as if it was just one array. What I would like to have is have each array appended on its own index, (withoug having to use a list, i want to use np arrays) i.e

temp = np.array([])
for i in my_items
   m = get_item_ids(i.color)  #returns an array as [1,4,20,5,3]  (always same number of items but diff ids
   temp = np.append(temp, m, axis=0)

On the second iteration lets suppose i get [5,4,15,3,10]

then i would like to have temp as array([1,4,20,5,3][5,4,15,3,10]) But instead i keep getting [1,4,20,5,3,5,4,15,3,10]

I am new to python but i am sure there is probably a way to concatenate in this way with numpy without using lists?

Why do you want to avoid lists?

hpaulj
– hpaulj

2021-01-31 21:16:39 +00:00
Commented Jan 31, 2021 at 21:16 — hpaulj
– hpaulj, Commented Jan 31, 2021 at 21:16

Salvatore Calcagno · Accepted Answer · 2021-01-31 20:42:57Z

1

You have to reshape m in order to have two dimension with

m.reshape(-1, 1)

thus adding the second dimension. Then you could concatenate along axis=1.

np.concatenate(temp, m, axis=1)

answered Jan 31, 2021 at 20:42

Salvatore Calcagno

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Comments

hpaulj · Accepted Answer · 2021-01-31 21:16:14Z

0

List append is much better - faster and easier to use correctly.

temp = []
for i in my_items
    m = get_item_ids(i.color)  #returns an array as [1,4,20,5,3]  (always same number of items but diff ids
    temp = m

Look at the list to see what it created. Then make an array from that:

 arr = np.array(temp)
 # or `np.vstack(temp)

answered Jan 31, 2021 at 21:16

hpaulj

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