Merge numpy arrays returned from loop

Question

I have a loop that generates numpy arrays:

for x in range(0, 1000):
   myArray = myFunction(x)

The returned array is always one dimensional. I want to combine all the arrays into one array (also one dimensional.

I tried the following, but it failed

allArrays = []
for x in range(0, 1000):
   myArray = myFunction(x)
   allArrays += myArray

The error is ValueError: operands could not be broadcast together with shapes (0) (9095). How can I get that to work?

For instance these two arrays:

[ 234 342 234 5454 34 6]
[ 23 2 1 4 55 34]

Shall be merge into this array:

[ 234 342 234 5454 34 6 23 2 1 4 55 34 ]

Answer 1

You probably mean

allArrays = np.array([])
for x in range(0, 1000):
    myArray = myFunction(x)
    allArrays = np.concatenate([allArrays, myArray])

A more concise approach (see wims answer) is to use a list comprehension,

allArrays = np.concatenate([myFunction(x) for x in range]) 

Answer 2

You should know the shape of returned array. Suppose, myArray.shape = (2, 4) Then

allArrays = np.empty((0, 4))
for x in range(0, 1000):
    myArray = myFunction(x)
    allArrays = np.append(allArrays, myArray, axis = 0)