Having an empty array
x = numpy.empty(0)
And two lists that looks like this
l1 = [1, 2, 3]
l2 = [4, 5, 6]
how do i add to the empty array the lists so that it becomes something like this
np.array([[1, 2, 3], [4, 5, 6])
instead of
np.array([1, 2, 3, 4, 5, 6])
which is what happens when i use
x = np.append(x, l1)
x = np.append(x, l2)
Simply use np.vstack to stack arrays in sequence vertically:
l1 = [1, 2, 3]
l2 = [4, 5, 6]
x = np.vstack([l1, l2])
print(x)
This results:
array([[1, 2, 3],
[4, 5, 6]])
import numpy as np
x = []
l1 = [1, 2, 3]
l2 = [4, 5, 6]
x.append(l1)
x.append(l2)
x = np.array(x)
print(x)
First of all convert the lists to numpy arrays to work more flexible
from numpy import *
l1 = [1, 2, 3]
l2 = [4, 5, 6]
l1_np = asarray(l1)
l2_np = asarray(l2)
l = concatenate([l1_np,l2_np])
You could use reshape to help make the append operation automatically
l1 = np.array([1, 2, 3])
l2 = np.array([4, 5, 6])
l=np.concatenate([l1,l2])
l.reshape((2,3))
outputs:
array([[1, 2, 3],
[4, 5, 6]])
x = np.array([l1, l2]), and in case you need to append frequently, I would suggest appending it to a list and then convert to array when you need to.np.appendis more expensive thatlist.append.x = numpy.empty(0)in the first place?np.appendthe code will be:x = np.empty((0,3));x = np.append(x, [l1], axis=0);x = np.append(x, [l2], axis=0)appenddocs carefully.enough!