Random choice from array in NumPy - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the numpy function np.random.choice() do?

It selects one or more random elements from a given array or list. You can choose with or without replacement.

beginner

How do you select 3 random elements from an array arr without repeating any element?

Use np.random.choice(arr, size=3, replace=False). The replace=False means no repeats.

beginner

What happens if you set replace=True in np.random.choice()?

Elements can be picked more than once. This means the same element can appear multiple times in the output.

intermediate

How can you assign different probabilities to elements when using np.random.choice()?

Use the p parameter with a list of probabilities that sum to 1. For example, p=[0.1, 0.9].

beginner

What is the default behavior of np.random.choice() if you do not specify size?

It returns a single random element from the array, not an array of elements.

What does np.random.choice(arr, size=5, replace=False) do?

A Returns the original array arr

B Selects 5 random elements from arr allowing repeats

C Selects 5 unique random elements from arr

D Selects 1 random element from arr

With replace=False, elements cannot repeat, so 5 unique elements are chosen.

How do you make sure elements can repeat when randomly choosing from an array?

A Set <code>replace=True</code>

B Set <code>replace=False</code>

C Set <code>size=1</code>

D Set <code>p=None</code>

Setting replace=True allows elements to be picked multiple times.

What parameter lets you give different chances to elements in np.random.choice()?

A <code>replace</code>

B <code>size</code>

C <code>arr</code>

D <code>p</code>

The p parameter is a list of probabilities for each element.

If you want only one random element from an array, what is the simplest call?

A <code>np.random.choice(arr)</code>

B <code>np.random.choice(arr, size=5)</code>

C <code>np.random.choice(arr, replace=False)</code>

D <code>np.random.choice(arr, p=[0.5, 0.5])</code>

By default, size is 1, so it returns one element.

What will happen if you try np.random.choice(arr, size=10, replace=False) but arr has only 5 elements?

A It will repeat elements to fill 10

B It will cause an error

C It will return 5 elements only

D It will return an empty array

Without replacement, you cannot pick more elements than exist, so it raises an error.

Explain how to use np.random.choice() to pick 4 random elements from an array with no repeats.

Think about the parameters controlling number and repetition.

Describe how to assign different probabilities to elements when randomly choosing from an array using numpy.

Look for the parameter that controls chances for each element.