Python - Check Whether One Array is a Subset of Another Array

Python – Check Whether One Array is a Subset of Another Array

In data structures and algorithms, checking if one array is a subset of another is a common problem. In Python, this task can be easily accomplished using built-in data types and methods.

This tutorial will explain the problem, provide sample input and output, outline solution steps, and Python program.

Problem Statement

Given two arrays, array1 and array2, determine whether all the elements of array2 are present in array1. In other words, check if array2 is a subset of array1.

Sample Input and Output

Example 1:

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# Input arrays
array1 = [1, 2, 3, 4, 5]
array2 = [2, 3, 5]

# Expected Output: True (array2 is a subset of array1)

Example 2:

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# Input arrays
array1 = [1, 2, 3]
array2 = [1, 2, 4]

# Expected Output: False (array2 is not a subset of array1)

Solution Approach

There are several ways to determine if one array is a subset of another in Python. Here are two common methods:

Using Sets: Convert both arrays to sets and use the issubset() method or the subset operator (<=). This is efficient and concise.
Using Loop and Membership Check: Iterate through the elements of the potential subset and check if each element exists in the larger array.

Python Program

Method 1: Using Sets

This method converts the arrays into sets and checks if the second set is a subset of the first. It is both concise and efficient.

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# Function to check if array2 is a subset of array1 using sets
def is_subset_set(array1, array2):
    return set(array2).issubset(set(array1))

# Test Example 1
array1 = [1, 2, 3, 4, 5]
array2 = [2, 3, 5]
print("Is array2 a subset of array1?", is_subset_set(array1, array2))  # Output: True

Method 2: Using Loop and Membership Check

This method iterates through each element of array2 and checks if it exists in array1. It is useful for understanding the underlying logic.

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# Function to check if array2 is a subset of array1 using a loop
def is_subset_loop(array1, array2):
    for element in array2:
        if element not in array1:
            return False
    return True

# Test Example 2
array1 = [1, 2, 3]
array2 = [1, 2, 4]
print("Is array2 a subset of array1?", is_subset_loop(array1, array2))  # Output: False

Conclusion

We explored two methods to check if one array is a subset of another in Python:

Using Sets: A concise and efficient approach using the built-in issubset() method.
Using a Loop: A more explicit method that checks membership for each element.

For most cases, using sets is recommended due to its simplicity and speed.

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Python – Check Whether One Array is a Subset of Another Array