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)

append an element to a specific row such as

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

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

retrieve an element from a specific row such as

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
– user2357112, Commented Oct 13, 2018 at 19:55
Possible duplicate of List of lists changes reflected across sublists unexpectedly — senior_mle
– senior_mle, Commented Oct 13, 2018 at 20:32

DanDeg · Accepted Answer · 2018-10-13 20:00:04Z

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, 2018 at 20:00

DanDeg

3161 gold badge2 silver badges7 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user3631926 Over a year ago

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]]

user2357112 Over a year ago

@user3631926: stackoverflow.com/questions/240178/…

Collectives™ on Stack Overflow

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

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related