CODEWITHSUNDEEP
pythonnumpy
Karnivaurus
Karnivaurus

Reputation: 24151

Adding rows to an empty 2D NumPy array

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?

Upvotes: 6

Views: 8115

Answers (2)

Riyaz
Riyaz

Reputation: 1470

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]])

Upvotes: 12

YXD
YXD

Reputation: 32521

>>> import numpy
>>> numpy.vstack(([1, 2], [8, 8]))
array([[1, 2],
       [8, 8]])

Upvotes: 0

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