Adding rows to an empty 2D NumPy array

Question

I want to start with an empty 2D NumPy array, and then add some rows to it. However, so far I have only been able to do this with a 1D array. Here is what I have tried so far:

a = numpy.array([])
a = numpy.append(a, [1, 2])
a = numpy.append(a, [8, 8])
print a

The output I get is:

[1, 2, 8, 8]

Whereas I want the output to be:

[[1, 2], [8, 8]]

How can I do this?

Answer 1

Try this:

>>> a = numpy.empty((0,2),int)
>>> a = numpy.append(a, [[1, 2]], axis=0)
>>> a = numpy.append(a, [[8, 8]], axis=0)
>>> a
array([[ 1,  2],
       [ 8,  8]])