Selecting NumPy array elements

From time to time, we will wish to select a specific constituent of an array. We will take a look at how to do this, but to kick off, let's make a 2x2 matrix again:

In: a = np.array([[1,2],[3,4]]) 
In: a 
Out: 
array([[1, 2], 
       [3, 4]]) 

The matrix was made this time by giving the array() function a list of lists. We will now choose each item of the matrix one at a time, as shown in the following code snippet. Recall that the index numbers begin from 0:

In: a[0,0] 
Out: 1 
In: a[0,1] 
Out: 2 
In: a[1,0] 
Out: 3 
In: a[1,1] 
Out: 4 

As you can see, choosing elements of an array is fairly simple. For the array a, we just employ the notation a[m,n], where m and n are the indices of the item in the array. Have a look at the following figure for your reference: