Numpy array dimension

Question

In [21]: a = np.array([1,2,3])

In [22]: a.shape
Out[22]: (3,)

What's the difference between (3,) and (3,1) in shape?

Why isn't the output (,3) or (1,3)? This is a 1 by 3 matrix, right?

This is a 1d array. not 1 X 3 matrix, a 1X3 matrix looks like [[1,2,3]]. — akuiper
– akuiper, Commented Dec 30, 2016 at 21:04

BrenBarn · Accepted Answer · 2016-12-30 21:04:31Z

2

No. A 1x3 matrix would be a two-dimensional array (e.g., np.array([[1, 2, 3]])). What you have is a one-dimensional array of length three. In mathematical terms, a 1D array roughly corresponds to a vector.

answered Dec 30, 2016 at 21:04

BrenBarn

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