What is the value of np.array(['a', 'b', 'c'])[2] ?

What is the value of np.zeros(6).size?

6

What values are printed by the following code?

x = np.array([2,4,6,8,10])

print(x[1:4])

4, 6, 8

What is the result of this code?

x = np.array([4,6,2,4,9,5])

x < 5

True, False,  True,  True, False, False

What is the result of this code?  (write 'error' if error)

x = np.array([4,6,2,4,9,5])

y = np.array([3])

x < y

False, False,  True, False, False, False

Even though the arrays have different sizes, broadcasting makes the result the same as if y = np.array([3,3,3,3,3,3,]).

What is the result of this code?

x = np.array([4, 6, 2, 5])

x[[True, True, False, True]]

array [4,6,5]

What is the result of this code?

x = np.array([4, 6, 2, 5])

x[x < 5]

array [4, 2]

What is the result of this code?

x = np.array([2, 0, 1, 6])

y = np.array([1, 2, 3, 4])

y[x < 2]

The array [2, 3]

What's the result of this code?  (say 'error' if an error)

x = np.array([4, 6, 2, 4, 9, 5])

x[[4,4,3]]

The array [5, 5, 9]

This is "fancy indexing", where an array (or list) is used to index into an array.

What's the result of this code?  (say 'error' if an error)

x = np.array([4, 6, 3, 12, 8, 1])

x[[np.ones(3)]]

The array [12, 12, 12].  

What's the result of this code?  (say 'error' if an error)

x = np.array([4, 6, 3, 12, 8, 1, 9])

x[x[1:3]]

Array [9, 12].

This is a tricky.  x[1:3] gives array [6,3].

x[[6,3]] is array [9, 12]

What's the result of this code?  (say 'error' if an error)

x = np.array([4, 6, 3, 12, 8, 1, 9])

x[4,2]

Error.

But x[[4,2]] gives array [8,3]

What's the result of this code?  (say 'error' if an error)

x = np.array([1.2, 2.3, -3.4, 4.5])

np.concat(x, x[x > 3])

It's an error, because the arrays to be concatenated need to be in a list (or tuple).

But this works: np.concat([x, x[x > 3]]).

What's the result of this code?  (say 'error' if an error)

x = np.array([3,2,1])

y = np.array([1,2,3])

np.concat([x,y,x])

Array [3,2,1,1,2,3,3,2,1]

What's the result of this code?  (say 'error' if an error)

x = np.array([3,2,1])

np.concat([x,x]).size

6

size gives the number of values in an array

What's the result of this code?  (say 'error' if an error)

np.arange(3) > 1

Array [False, False, True]

What is the result of this code?

x = np.array([4, 6, 2, 5])

x[x < 5]

array [4, 2]