numpy - Syntax in Python (.T)

Question

In the help resource for the multivariate normal sampling function in SciPy, they give the following example:

x,y = np.random.multivariate_normal(mean,cov,5000).T

My question is rather basic: what does the final .T actually do?

Thanks a lot, I know it is fairly simple, but it is hard to look in Google for ".T".

Answer 1

The .T accesses the attribute T of the object, which happens to be a NumPy array. The T attribute is the transpose of the array, see the documentation.

Apparently you are creating random coordinates in the plane. The output of multivariate_normal() might look like this:

>>> np.random.multivariate_normal([0, 0], [[1, 0], [0, 1]], 5)  
array([[ 0.59589335,  0.97741328],
       [-0.58597307,  0.56733234],
       [-0.69164572,  0.17840394],
       [-0.24992978, -2.57494471],
       [ 0.38896689,  0.82221377]])

The transpose of this matrix is:

array([[ 0.59589335, -0.58597307, -0.69164572, -0.24992978,  0.38896689],
       [ 0.97741328,  0.56733234,  0.17840394, -2.57494471,  0.82221377]])

which can be conveniently separated in x and y parts by sequence unpacking.