Creating boolean arrays in NumPy - Quick Revision & Summary

Recall & Review

beginner

What is a boolean array in numpy?

A boolean array in numpy is an array where each element is either True or False. It is often used for filtering or masking data.

beginner

How do you create a boolean array from a numpy array based on a condition?

You apply a condition directly to a numpy array, which returns a boolean array. For example, arr > 5 returns True for elements greater than 5 and False otherwise.

beginner

What numpy function can create a boolean array filled with True or False?

You can use numpy.ones(shape, dtype=bool) to create a boolean array filled with True, or numpy.zeros(shape, dtype=bool) to create one filled with False.

beginner

How can boolean arrays help in real-life data filtering?

Boolean arrays let you select or ignore data easily. For example, in a list of temperatures, you can create a boolean array to find all days hotter than 30°C and then extract those days' data.

beginner

What does the expression arr % 2 == 0 return when applied to a numpy array?

It returns a boolean array where each element is True if the corresponding element in arr is even, and False if it is odd.

What type of values does a numpy boolean array contain?

A Integers

B True or False

C Strings

D Floats

Boolean arrays contain only True or False values.

Which numpy function creates a boolean array filled with False?

A numpy.zeros(shape, dtype=bool)

B numpy.ones(shape, dtype=bool)

C numpy.empty(shape, dtype=bool)

D numpy.full(shape, True)

numpy.zeros(shape, dtype=bool) creates a boolean array filled with False.

What does the expression arr > 10 return?

A A boolean array where elements are True if > 10

B An array of numbers greater than 10

C A sum of elements greater than 10

D An error

Applying a condition returns a boolean array indicating which elements satisfy it.

How can boolean arrays be used in data filtering?

A To change data types

B To create new columns

C To select elements that meet a condition

D To sort data

Boolean arrays help select elements that meet specific conditions.

What is the dtype of a boolean numpy array?

A int

B float

C str

D bool

Boolean arrays have dtype 'bool' in numpy.

Explain how to create a boolean array from a numpy array using a condition. Give a simple example.

Think about how you check if numbers are bigger than a value.

Describe two ways to create boolean arrays in numpy and when you might use each.

One way uses existing data, the other creates new arrays filled with True or False.