Concatenating Numpy array to Numpy array of arrays

Question

I'm trying to make a for loop that each time adds an array, to the end of an array of arrays and I can't quite put my finger on how to. The general idea of the program:

for x in range(0,longnumber):
    generatenewarray
    add new array to end of array

So for example, the output of:

newArray = [1,2,3]
array  = [[1,2,3,4],[1,4,3]]

would be: [[1,2,3,4],[1,4,3],[1,2,3]]

If the wording is poor let me know and I can try and edit it to be better!

gariepy · Accepted Answer · 2015-12-08 23:43:48Z

1

Is this what you need?

list_of_arrays = []
for x in range(0,longnumber):
    a = generatenewarray
    list_of_arrays.append(a)

answered Dec 8, 2015 at 23:43

gariepy

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3 Comments

Danny Over a year ago

It's a numpy array and needs to return one, so apparend doesn't work I don't think.

gariepy Over a year ago

well, your problem doesn't seem well-formed then, as your arrays have different dimensions, and the only way you could concatenate them would be to make a 1xN array, which I'm guessing is not what you want. If your individual arrays actually are the same size, then try numpy.vstack() mentioned above. big_array = numpy.vstack( (big_array, new_array))...note that growing arrays like this isn't exactly efficient...

hpaulj Over a year ago

Better to append to a list. If it must be an array (object dtype), convert it at the end.

Daniel R. Hunter · Accepted Answer · 2015-12-09 01:19:08Z

0

It's not pretty, but this will work. You turn both numpy arrays into lists, add those two lists, and finally convert the result into a new numpy array:

np.array(array.tolist() + newArray.tolist())

answered Dec 9, 2015 at 1:19

Daniel R. Hunter

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