Python Numpy append array without flattening

Question

In Python 3 I am importing several data files in a loop, and I would like to be able to store all the data in a single 2-dimensional array. I start with something like data = np.array([]) and on each iteration i want to add a new array datai = np.array([1,2,3]), how can I get my final array to look like this? [[1,2,3],[1,2,3],...,[1,2,3]]

I have tried np.append, np.concatenate, and np.stack, but none seem to work. An example code that I'm trying:

data = np.array([])
for i in range(datalen):
    datai = *func to load data as array*
    data = np.append(data, datai)

but of course this returns a flattened array. Is there any way I can get back a 2-dimensional array of length datalen with each element being the array datai?

Thanks!

Answer 1

The fastest way would be vstack

data = np.vstack((get_data() for i in range(datalen)))

vstack requires a tuple/iterable

data = np.vstack((data1, data2, data3))

or you can do this by appending with axis=0

data = np.empty(shape=(0, 3))
data = np.append(data, datai.reshape((-1, 3)), axis=0)  # -1 will make the rows automatic