Python: Union of sets

Python sets: Exercise-7 with Solution

Write a Python program to create a union of sets.

From Wikipedia,
In set theory, the union (denoted by ∪) of a collection of sets is the set of all elements in the collection. It is one of the fundamental operations through which sets can be combined and related to each other. A nullary union refers to a union of zero (0) sets and it is by definition equal to the empty set.

The union of two sets A and B is the set of elements which are in A, in B, or in both A and B. In symbols,
A ∪ B = {x : x ∈ A or x ∈ B}
For example, if A = {1, 3, 5, 7} and B = {1, 2, 4, 6, 7} then A ∪ B = {1, 2, 3, 4, 5, 6, 7}. A more elaborate example (involving two infinite sets) is:
A = {x is an even integer larger than 1}
B = {x is an odd integer larger than 1}
A ∪ B = {2,3,4,5,6,...}


As another example, the number 9 is not contained in the union of the set of prime numbers {2, 3, 5, 7, 11, ...} and the set of even numbers {2, 4, 6, 8, 10, ...}, because 9 is neither prime nor even.
Sets cannot have duplicate elements, so the union of the sets {1, 2, 3} and {2, 3, 4} is {1, 2, 3, 4}. Multiple occurrences of identical elements have no effect on the cardinality of a set or its contents.

Sample Solution-1:

Using union() function

Python Code:

setc1 = set(["green", "blue"])
setc2 = set(["blue", "yellow"])
print("Original sets:")
print(setc1)
print(setc2)
setc = setc1.union(setc2)
print("\nUnion of above sets:")
print(setc)
setn1 = set([1, 1, 2, 3, 4, 5])
setn2 = set([1, 5, 6, 7, 8, 9])
print("\nOriginal sets:")
print(setn1)
print(setn2)
print("\nUnion of above sets:")
setn = setn1.union(setn2)
print(setn)

Sample Output:

Original sets:
{'blue', 'green'}
{'blue', 'yellow'}

Union of above sets:
{'blue', 'yellow', 'green'}

Original sets:
{1, 2, 3, 4, 5}
{1, 5, 6, 7, 8, 9}

Union of above sets:
{1, 2, 3, 4, 5, 6, 7, 8, 9}

Pictorial Presentation:

Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Sample Solution-2:

Using | operator

Python Code:

setc1 = set(["green", "blue"])
setc2 = set(["blue", "yellow"])
print("Original sets:")
print(setc1)
print(setc2)
setc = setc1 | setc2
print("\nUnion of above sets:")
print(setc)
setn1 = set([1, 1, 2, 3, 4, 5])
setn2 = set([1, 5, 6, 7, 8, 9])
print("\nOriginal sets:")
print(setn1)
print(setn2)
print("\nUnion of above sets:")
setn = setn1 | setn2
print(setn)

Sample Output:

Original sets:
{'green', 'blue'}
{'blue', 'yellow'}

Union of above sets:
{'green', 'yellow', 'blue'}

Original sets:
{1, 2, 3, 4, 5}
{1, 5, 6, 7, 8, 9}

Union of above sets:
{1, 2, 3, 4, 5, 6, 7, 8, 9}

Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Sample Solution-3:

Union of more than two sets:

Python Code:

setn1 = set([1, 1, 2, 3, 4, 5])
setn2 = set([1, 5, 6, 7, 8, 9])
setn3 = set([3, 4, 5, 3, 9, 10])
setn4 = set([5, 7, 9, 10, 12, 14])

print("\nOriginal sets:")
print(setn1)
print(setn2)
print(setn3)
print(setn4)
print("\nUnion of first three sets:")
setn = setn1.union(setn2, setn3)
print(setn)
print("\nUnion of above four sets:")
setn = setn1.union(setn2, setn3, setn4)
print(setn)

Sample Output:

Original sets:
{1, 2, 3, 4, 5}
{1, 5, 6, 7, 8, 9}
{3, 4, 5, 9, 10}
{5, 7, 9, 10, 12, 14}

Union of first three sets:
{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

Union of above four sets:
{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14}

Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Python Code Editor:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous: Write a Python program to create an intersection of sets.
Next: Write a Python program to create set difference.