# Shared Flashcard Set

## Details

NumPy arrays
NumPy arrays, Python
18
Computer Science
02/14/2021

Term
 What is the value of np.array(['a', 'b', 'c'])[2] ?
Definition
 'b'
Term
 What is the value of np.zeros(6).size?
Definition
 6
Term
 Write code to get the 2nd and 3rd elements of array x.
Definition
 x[[1,2]]
Term
 What values are printed by the following code? x = np.array([2,4,6,8,10]) print(x[1:4])
Definition
 4, 6, 8
Term
 What is the result of this code? x = np.array([4,6,2,4,9,5]) x < 5
Definition
 True, False,  True,  True, False, False
Term
 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
Definition
 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,]).
Term
 What is the result of this code?   x = np.array([4, 6, 2, 5]) x[[True, True, False, True]]
Definition
 array [4,6,5]
Term
 What is the result of this code?   x = np.array([4, 6, 2, 5]) x[x < 5]
Definition
 array [4, 2]
Term
 What is the result of this code?   x = np.array([2, 0, 1, 6]) y = np.array([1, 2, 3, 4]) y[x < 2]
Definition
 The array [2, 3]
Term
 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]]
Definition
 The array [5, 5, 9]   This is "fancy indexing", where an array (or list) is used to index into an array.
Term
 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)]]
Definition
 The array [12, 12, 12].
Term
 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]]
Definition
 Array [9, 12].   This is a tricky.  x[1:3] gives array [6,3]. x[[6,3]] is array [9, 12]
Term
 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]
Definition
 Error.   But x[[4,2]] gives array [8,3]
Term
 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])
Definition
 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]]).
Term
 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])
Definition
 Array [3,2,1,1,2,3,3,2,1]
Term
 What's the result of this code?  (say 'error' if an error)   x = np.array([3,2,1]) np.concat([x,x]).size
Definition
 6   size gives the number of values in an array
Term
 What's the result of this code?  (say 'error' if an error)   np.arange(3) > 1
Definition
 Array [False, False, True]
Term
 What is the result of this code?   x = np.array([4, 6, 2, 5]) x[x < 5]
Definition
 array [4, 2]
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