Comparison operations in NumPy - Mini Project: Build & Apply

Comparison operations

📖 Scenario: You work in a store that tracks daily sales numbers. You want to find which days had sales above a certain target.

🎯 Goal: Build a small program using numpy to compare daily sales numbers against a sales target and find which days met or exceeded the target.

📋 What You'll Learn

Use numpy arrays to store sales data

Create a sales target variable

Use comparison operations to find days with sales >= target

Print the boolean array showing which days met the target

💡 Why This Matters

🌍 Real World

Stores and businesses often compare daily sales or performance numbers against targets to see which days did well.

💼 Career

Data analysts and scientists use comparison operations to filter and analyze data quickly and efficiently.

1

Create the sales data array

Create a numpy array called sales with these exact daily sales numbers: 120, 85, 90, 150, 110.

NumPy

import numpy as np
# Create the numpy array called sales with the given numbers
# Your code here

Hint

Use np.array([...]) to create the array with the exact numbers.

2

Set the sales target

Create a variable called target and set it to the integer 100.

NumPy

import numpy as np
sales = np.array([120, 85, 90, 150, 110])
# Create the variable target and set it to 100
# Your code here

Hint

Just assign the number 100 to the variable target.

3

Compare sales to the target

Create a variable called above_target that stores the result of comparing sales to target using the >= operator.

NumPy

import numpy as np
sales = np.array([120, 85, 90, 150, 110])
target = 100
# Create above_target using sales >= target
# Your code here

Hint

Use the >= operator between the sales array and the target variable.

4

Print the comparison result

Print the variable above_target to show which days had sales greater than or equal to the target.

NumPy

import numpy as np
sales = np.array([120, 85, 90, 150, 110])
target = 100
above_target = sales >= target
# Print above_target
# Your code here

Hint

Use print(above_target) to display the boolean array.

Practice

1. What does the numpy expression arr == 5 return when arr is a numpy array?

easy

A. The sum of all elements equal to 5

B. An array of True/False values showing where elements equal 5

C. The count of elements equal to 5

D. A single True or False value

Solution

1. Step 1: Understand element-wise comparison

   The expression arr == 5 compares each element of the array to 5 individually.

2. Step 2: Result type of comparison

   This returns a new array of the same shape with True where the element equals 5, and False otherwise.

3. Final Answer:

   An array of True/False values showing where elements equal 5 -> Option B

4. Quick Check:

   Element-wise comparison = Boolean array [OK]

Hint: Remember == returns True/False array element-wise [OK]

Common Mistakes:

• Thinking it returns a count or sum
• Expecting a single True/False value
• Confusing == with assignment =

2. Which of the following is the correct syntax to check if elements in numpy array arr are greater than 10?

easy

A. arr >> 10

B. arr => 10

C. arr > 10

D. arr >= 10

Solution

1. Step 1: Identify correct comparison operator

   The operator for 'greater than' is >, so arr > 10 checks elements greater than 10.

2. Step 2: Check other options

   arr => 10 is invalid syntax, arr >> 10 is a bitwise shift, and arr >= 10 checks greater or equal, not strictly greater.

3. Final Answer:

   arr > 10 -> Option C

4. Quick Check:

   Greater than operator is > [OK]

Hint: Use > for greater than, >= for greater or equal [OK]

Common Mistakes:

• Using => instead of >
• Confusing bitwise >> with comparison
• Using >= when > is asked

3. What is the output of the following code?

import numpy as np
arr = np.array([3, 7, 2, 9])
result = arr >= 5
print(result)

medium

A. [False False False False]

B. [True False True False]

C. [True True True True]

D. [False True False True]

Solution

1. Step 1: Compare each element with 5

   Elements: 3, 7, 2, 9. Check if each is >= 5: 3>=5 is False, 7>=5 is True, 2>=5 is False, 9>=5 is True.

2. Step 2: Form boolean array

   The result is [False, True, False, True].

3. Final Answer:

   [False True False True] -> Option D

4. Quick Check:

   Element-wise >= 5 = [False True False True] [OK]

Hint: Check each element against 5 carefully [OK]

Common Mistakes:

• Mixing up >= with >
• Misreading element values
• Expecting integer output instead of boolean

4. Identify the error in this numpy comparison code:

import numpy as np
arr = np.array([1, 2, 3])
result = arr = 2
print(result)

medium

A. Using single = instead of == for comparison

B. Array must be converted to list before comparison

C. print() cannot display numpy arrays

D. Missing parentheses in print statement

Solution

1. Step 1: Check comparison syntax

   The code uses arr = 2 which assigns 2 to arr, not compares. Comparison needs ==.

2. Step 2: Understand effect of assignment

   Assignment overwrites arr with 2, so print(result) prints 2, not a boolean array.

3. Final Answer:

   Using single = instead of == for comparison -> Option A

4. Quick Check:

   Comparison needs ==, not = [OK]

Hint: Use == for comparison, = is assignment [OK]

Common Mistakes:

• Confusing = and ==
• Thinking print can't show arrays
• Believing arrays must convert to lists

5. Given two numpy arrays:

import numpy as np
arr1 = np.array([1, 4, 6, 8])
arr2 = np.array([2, 4, 5, 10])

Which expression returns a boolean array showing where elements in arr1 are less than or equal to elements in arr2?

hard

A. arr1 <= arr2

B. arr1 < arr2

C. arr1 == arr2

D. arr1 >= arr2

Solution

1. Step 1: Understand element-wise comparison between arrays

   Comparing two arrays with operators like <= compares each element pair at the same index.

2. Step 2: Identify operator for 'less than or equal'

   The operator <= checks if elements in arr1 are less than or equal to corresponding elements in arr2.

3. Final Answer:

   arr1 <= arr2 -> Option A

4. Quick Check:

   Use <= for less or equal element-wise [OK]

Hint: Use <= to compare arrays element-wise for less or equal [OK]

Common Mistakes:

• Using < instead of <= when equal counts
• Using == which only checks equality
• Using >= which is opposite