Indexing of ndarrays

Array indexing refers to the way of accessing a particular array element or elements. In NumPy, all ndarray indices are zero-based—that is, the first item of an array has index 0. Negative indices are understood as counting from the end of the array.

Direct access to an ndarray's element

Direct access to a single ndarray's element is one of the most used forms of access.

The following code builds a 3 x 3 random-valued ndarray for our use:

arr = np.random.randn(3,3); 
arr

The arr ndarray has the following elements:

array([[-0.04113926, -0.273338  , -1.05294723],
       [ 1.65004669, -0.09589629,  0.15586867],
       [ 0.39533427,  1.47193681,  0.32148741]])

We can index the first element with integer index 0, as follows:

arr[0]

This gives us the first row of the arr ndarray, as follows:

array([-0.04113926, ...