Curious2learn Curious2learn - 1 year ago 338
Python Question

initialize a numpy array

Is there way to initialize a numpy array of a shape and add to it? I will explain what I need with a list example. If I want to create a list of objects generated in a loop, I can do:

a = []
for i in range(5):

I want to do something similar with a numpy array. I know about vstack, concatenate etc. However, it seems these require two numpy arrays as inputs. What I need is:

big_array # Initially empty. This is where I don't know what to specify
for i in range(5):
array i of shape = (2,4) created.
add to big_array

should have a shape
. How to do this? Thanks for your help.

EDIT: I want to add the following clarification. I am aware that I can define
big_array = numpy.zeros((10,4))
and then fill it up. However, this requires specifying the size of big_array in advance. I know the size in this case, but what if I do not? When we use the
function for extending the list in python, we don't need to know its final size in advance. I am wondering if something similar exists for creating a bigger array from smaller arrays, starting with an empty array. Thanks!

Answer Source


Return a new array of given shape and type, filled with zeros.



Return a new array of given shape and type, filled with ones.



Return a new array of given shape and type, without initializing entries.

However, the mentality in which we construct an array by appending elements to a list is not much used in numpy, because it's less efficient (numpy datatypes are much closer to the underlying C arrays). Instead, you should preallocate the array to the size that you need it to be, and then fill in the rows. You can use numpy.append if you must, though.

Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download