np.zeros() for zero-filled arrays in NumPy - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does np.zeros() do in NumPy?

np.zeros() creates a new array filled with zeros. You specify the shape (size) of the array, and it returns an array of that shape with all elements set to zero.

beginner

How do you create a 3x3 zero-filled array using np.zeros()?

Use np.zeros((3, 3)). The argument is a tuple representing the shape: 3 rows and 3 columns.

beginner

What data type does np.zeros() use by default?

By default, np.zeros() creates an array of floats (floating-point numbers).

intermediate

How can you create a zero-filled array of integers using np.zeros()?

Use the dtype parameter: np.zeros((3, 3), dtype=int) creates a 3x3 array of zeros as integers.

beginner

Why might you use np.zeros() in data science?

It helps to initialize arrays before filling them with data or results. For example, creating empty containers for calculations or placeholders for missing data.

What is the output of np.zeros(5)?

A [0 0 0 0 0]

B [1 1 1 1 1]

C [5 5 5 5 5]

D An error

np.zeros(5) creates a 1D array of length 5 filled with zeros.

How do you specify the shape of a 2D zero array with 4 rows and 2 columns?

A np.zeros((4, 2))

B np.zeros([4, 2])

C np.zeros(4, 2)

D np.zeros{4, 2}

The shape must be a tuple, so np.zeros((4, 2)) is correct.

What is the default data type of elements in np.zeros()?

A int

B str

C float

D bool

By default, np.zeros() creates arrays of floats.

Which parameter changes the data type of zeros in np.zeros()?

A type

B shape

C size

D dtype

The dtype parameter sets the data type of the array elements.

Why use np.zeros() instead of a Python list of zeros?

A NumPy arrays are slower but prettier

B NumPy arrays are faster and use less memory

C Python lists cannot hold zeros

D Python lists do not support zeros

NumPy arrays are optimized for numerical operations, making them faster and more memory efficient than Python lists.

Explain how to create a zero-filled 2D array with 5 rows and 4 columns using np.zeros(). Include how to specify the data type as integers.

Remember the shape is a tuple and use dtype=int.

Describe three common reasons why data scientists use np.zeros() when working with data.

Think about starting points for data or results.

Practice

1. What does the np.zeros() function do in NumPy?

easy

A. Creates an array filled with zeros

B. Creates an array filled with ones

C. Creates an array with random values

D. Creates an empty array with no elements

Solution

1. Step 1: Understand the purpose of np.zeros()

   This function is designed to create arrays where every element is zero.

2. Step 2: Compare with other array creation functions

   Unlike np.ones() or random array functions, np.zeros() specifically fills the array with zeros.

3. Final Answer:

   Creates an array filled with zeros -> Option A

4. Quick Check:

   np.zeros() = zero-filled array [OK]

Hint: Remember zeros means all elements are zero [OK]

Common Mistakes:

• Confusing with np.ones()
• Thinking it creates empty arrays
• Assuming it creates random values

2. Which of the following is the correct syntax to create a 3x3 zero-filled array using NumPy?

easy

A. np.zeros(3,3)

B. np.zeros[3,3]

C. np.zeros((3,3))

D. np.zeros{3,3}

Solution

1. Step 1: Check the shape argument format

   The shape must be passed as a tuple, so it should be (3,3).

2. Step 2: Validate the function call syntax

   Only parentheses () are valid for function calls, so np.zeros((3,3)) is correct.

3. Final Answer:

   np.zeros((3,3)) -> Option C

4. Quick Check:

   Shape as tuple inside parentheses [OK]

Hint: Use double parentheses for shape tuple [OK]

Common Mistakes:

• Using commas without tuple
• Using square or curly brackets
• Missing parentheses

3. What is the output of the following code?

import numpy as np
arr = np.zeros(4, dtype=int)
print(arr)

medium

A. [0 0 0 0]

B. [0. 0. 0. 0.]

C. [1 1 1 1]

D. [False False False False]

Solution

1. Step 1: Understand np.zeros(4, dtype=int)

   This creates a 1D array of length 4 filled with zeros, with integer type.

2. Step 2: Check the printed output format

   Since dtype is int, zeros are printed as integers without decimal points.

3. Final Answer:

   [0 0 0 0] -> Option A

4. Quick Check:

   Integer zeros printed without decimals [OK]

Hint: dtype=int means zeros print as integers [OK]

Common Mistakes:

• Expecting float zeros with decimals
• Confusing with ones array
• Thinking output is boolean

4. Identify the error in this code snippet:

import numpy as np
arr = np.zeros[5]
print(arr)

medium

A. Missing dtype argument

B. Using square brackets instead of parentheses for function call

C. Shape argument should be a tuple

D. np.zeros cannot create 1D arrays

Solution

1. Step 1: Check function call syntax

   Functions in Python require parentheses (), not square brackets [].

2. Step 2: Confirm correct usage of np.zeros

   The shape argument can be an integer for 1D arrays, so 5 is valid.

3. Final Answer:

   Using square brackets instead of parentheses for function call -> Option B

4. Quick Check:

   Function calls need parentheses [OK]

Hint: Use () for functions, not [] [OK]

Common Mistakes:

• Using [] instead of ()
• Thinking dtype is mandatory
• Confusing shape tuple for 1D arrays

5. You want to create a zero-filled 2D array with 3 rows and 4 columns, but the array must store boolean values. Which code is correct?

hard

A. np.zeros((3,4), type=bool)

B. np.zeros(3,4, dtype=bool)

C. np.zeros([3,4], dtype=bool)

D. np.zeros((3,4), dtype=bool)

Solution

1. Step 1: Check shape argument format

   The shape must be a tuple, so (3,4) is correct.

2. Step 2: Verify dtype argument name and value

   The correct keyword is dtype, and bool is valid to create boolean arrays.

3. Step 3: Eliminate incorrect options

   Using the wrong keyword type instead of dtype, passing shape as separate arguments like np.zeros(3,4, dtype=bool) without tuple parentheses, using a list [3,4] instead of tuple.

4. Final Answer:

   np.zeros((3,4), dtype=bool) -> Option D

5. Quick Check:

   Shape tuple and dtype=bool required [OK]

Hint: Use tuple for shape and dtype=bool for boolean zeros [OK]

Common Mistakes:

• Passing shape as separate args
• Using list instead of tuple
• Wrong keyword 'type' instead of 'dtype'