What does .shape[] do in “for i in range(Y.shape[0])”?

Question

I'm trying to break down a program line by line. Y is a matrix of data but I can't find any concrete data on what .shape[0] does exactly.

for i in range(Y.shape[0]): 

if Y[i] == -1:

This program uses numpy, scipy, matplotlib.pyplot, and cvxopt.

Answer 1

The shape attribute for numpy arrays returns the dimensions of the array. If Y has n rows and m columns, then Y.shape is (n,m). So Y.shape[0] is n.

>>Y = np.arange(12).reshape(3,4) 

>>print(Y) 

array([[ 0, 1, 2, 3], [ 4, 5, 6, 7], [ 8, 9, 10, 11]]) 

>>Y.shape 

(3, 4) 

>>Y.shape[0] 

3

To know more about this you can have a look at the following video tutorial:-