np.round(), np.floor(), np.ceil() in NumPy - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does np.round() do in numpy?

np.round() rounds each number in an array to the nearest integer or to a specified number of decimal places.

beginner

Explain the function of np.floor().

np.floor() takes each number in an array and rounds it down to the nearest whole number (integer) less than or equal to the number.

beginner

What does np.ceil() do?

np.ceil() rounds each number in an array up to the nearest whole number (integer) greater than or equal to the number.

intermediate

How does np.round() differ from np.floor() and np.ceil()?

np.round() rounds to the nearest integer (up or down), while np.floor() always rounds down and np.ceil() always rounds up.

beginner

If you have the number 3.7, what will np.round(), np.floor(), and np.ceil() return?

np.round(3.7) returns 4.0
np.floor(3.7) returns 3.0
np.ceil(3.7) returns 4.0

What does np.floor(2.9) return?

A 2.9

B 3.0

C 2.0

D 3.9

np.floor() rounds down to the nearest integer, so 2.9 becomes 2.0.

Which function rounds numbers to the nearest integer, either up or down?

A np.round()

B np.floor()

C np.ceil()

D None of these

np.round() rounds to the nearest integer, up or down depending on the decimal.

What will np.ceil(-1.2) return?

A -2.0

B -0.0

C -1.2

D -1.0

np.ceil() rounds up to the nearest integer. For negative numbers, 'up' means closer to zero, so -1.2 becomes -1.0.

How can you round numbers in a numpy array to 2 decimal places?

A np.round(array, 2)

B np.floor(array, 2)

C np.ceil(array, 2)

D np.round(array)

Use np.round() with the second argument as the number of decimals, like 2.

Which function always rounds numbers up?

A np.floor()

B np.ceil()

C np.round()

D np.trunc()

np.ceil() always rounds numbers up to the nearest integer.

Describe the difference between np.round(), np.floor(), and np.ceil() with examples.

Think about how each function treats decimals differently.

Explain how you would round all numbers in a numpy array to 1 decimal place using numpy functions.

Look for a function that allows decimal precision.

Practice

1. What does the function np.floor() do to a decimal number?

easy

A. Rounds the number down to the nearest whole number

B. Rounds the number up to the nearest whole number

C. Rounds the number to the nearest integer based on decimals

D. Leaves the number unchanged

Solution

1. Step 1: Understand the behavior of np.floor()

   It always rounds any decimal number down to the nearest whole number, regardless of the decimal part.

2. Step 2: Compare with other rounding functions

   Unlike np.ceil() which rounds up, np.floor() always rounds down.

3. Final Answer:

   Rounds the number down to the nearest whole number -> Option A

4. Quick Check:

   np.floor(3.7) = 3 [OK]

Hint: Floor always rounds down, no matter the decimal [OK]

Common Mistakes:

• Confusing floor with ceil
• Thinking floor rounds to nearest integer
• Assuming floor changes only if decimal > 0.5

2. Which of the following is the correct syntax to round the array arr = np.array([1.2, 2.5, 3.7]) to 1 decimal place using np.round()?

easy

A. np.round(arr, decimals=0.1)

B. np.round(arr, decimals=1)

C. np.round(arr, 0)

D. np.round(arr, places=1)

Solution

1. Step 1: Check np.round() parameter for decimals

   The parameter to specify decimal places is named 'decimals' and expects an integer.

2. Step 2: Validate each option

   A: decimals=0.1 invalid (must be integer). B: np.round(arr, 0) rounds to 0 decimal places. C: np.round(arr, decimals=1) correct. D: 'places' not a valid parameter.

3. Final Answer:

   np.round(arr, decimals=1) -> Option B

4. Quick Check:

   np.round(arr, decimals=1) rounds to 1 decimal [OK]

Hint: Use decimals=number to set decimal places in np.round() [OK]

Common Mistakes:

• Using wrong parameter name like 'places'
• Passing float instead of int for decimals
• Omitting decimals parameter and expecting decimal rounding

3. What is the output of the following code?

import numpy as np
arr = np.array([1.7, 2.3, 3.5])
result = np.ceil(arr)
print(result)

medium

A. [2. 3. 4.]

B. [2. 2. 3.]

C. [1. 3. 4.]

D. [1. 2. 3.]

Solution

1. Step 1: Understand np.ceil() behavior on each element

   np.ceil() rounds each number up to the nearest whole number: 1.7 -> 2, 2.3 -> 3, 3.5 -> 4.

2. Step 2: Apply np.ceil() to the array

   The resulting array is [2., 3., 4.].

3. Final Answer:

   [2. 3. 4.] -> Option A

4. Quick Check:

   np.ceil rounds decimals up [OK]

Hint: Ceil always rounds decimals up to next integer [OK]

Common Mistakes:

• Confusing ceil with floor
• Expecting rounding to nearest integer
• Ignoring decimal part in output

4. The following code throws an error. What is the mistake?

import numpy as np
arr = np.array([1.2, 2.5, 3.7])
result = np.round(arr, decimal=1)
print(result)

medium

A. np.round() requires the second argument to be a string

B. np.round() cannot round arrays

C. The array must be integers to use np.round()

D. The parameter name should be 'decimals' not 'decimal'

Solution

1. Step 1: Identify the parameter name error

   The correct parameter name for decimal places in np.round() is 'decimals', not 'decimal'.

2. Step 2: Confirm np.round() usage

   np.round() works on numpy arrays and accepts an integer for decimals parameter.

3. Final Answer:

   The parameter name should be 'decimals' not 'decimal' -> Option D

4. Quick Check:

   Use decimals=1, not decimal=1 [OK]

Hint: Remember parameter is 'decimals', plural, in np.round() [OK]

Common Mistakes:

• Using 'decimal' instead of 'decimals'
• Thinking np.round() only works on scalars
• Passing string instead of integer for decimals

5. You have the array arr = np.array([1.25, 2.75, 3.5, 4.1]). You want to round each number to the nearest integer but always round .5 up. Which combination of numpy functions will achieve this?

hard

A. Use np.round(arr)

B. Use np.ceil(arr - 0.5)

C. Use np.floor(arr + 0.5)

D. Use np.round(arr, decimals=0)

Solution

1. Step 1: Understand rounding .5 up behavior

   Standard np.round() rounds .5 to nearest even integer, not always up.

2. Step 2: Use floor with offset to force .5 up rounding

   Adding 0.5 then applying np.floor() rounds numbers so that .5 always rounds up.

3. Step 3: Check example

   1.25 + 0.5 = 1.75 floor = 1, 2.75 + 0.5 = 3.25 floor = 3, 3.5 + 0.5 = 4.0 floor = 4, 4.1 + 0.5 = 4.6 floor = 4.

4. Final Answer:

   Use np.floor(arr + 0.5) -> Option C

5. Quick Check:

   Floor after adding 0.5 rounds .5 up [OK]

Hint: Add 0.5 then floor to always round .5 up [OK]

Common Mistakes:

• Using np.round() which rounds .5 to nearest even
• Using ceil incorrectly with subtraction
• Ignoring .5 rounding behavior