python numpy dynamically add elements to the end of a specific row

Question

I want to do the following using numpy:

create an an array of arrays using numpy where each row contains only one element such as

[[0],[0],[0],[0],[0],[0],[0],[0],[0],[0]]

xx = np.array([np.array([0])] * 10)

[[0],[0,5],[0],[0],[0],[0],[0],[0],[0],[0]]

xx[1] = np.append(xx[1],5)

print(x[1,1])

this means that I need a two dimensional array with different row size and the elements are appended dynamically

That is not the kind of thing NumPy is designed for. Consider using a list of lists. — user2357112, Oct 13 '18 at 19:55
Possible duplicate of [List of lists changes reflected across sublists unexpectedly](https://stackoverflow.com/questions/240178/list-of-lists-changes-reflected-across-sublists-unexpectedly) — senior_mle, Oct 13 '18 at 20:32

score 1 · Answer 1 · answered Oct 13 '18 at 20:00

1

If using a lists inside a list, you can create it like this

l = [[0],[0],[0],[0],[0],[0],[0],[0],[0],[0]]

And if you want to append something, just use

l[1].append(4)

You will get:

[[0],[0,4],[0],[0],[0],[0],[0],[0],[0],[0]]

And if you want to access the new element:

l[1][1]

Which will return:

answered Oct 13 '18 at 20:00

DanDeg

Thanks. But when I use l = [[0]]*10 instead of l = [[0],[0],[0],[0],[0],[0],[0],[0],[0],[0]] the second line (l[1].append(4)) adds the value 4 to all generating [[0, 4], [0, 4], [0, 4], [0, 4], [0, 4], [0, 4], [0, 4], [0, 4], [0, 4], [0, 4]] – user3631926 Oct 13 '18 at 20:13
@user3631926: https://stackoverflow.com/questions/240178/list-of-lists-changes-reflected-across-sublists-unexpectedly – user2357112 Oct 13 '18 at 20:15

1 Answers1