Creating A New List For Each For Loop
Last Updated :
29 Dec, 2024
In Python, creating new lists inside a for
loop is an approach that is commonly used to manage and process data during iterations. This allows us to generate new lists for each loop iteration, ensuring that data remains isolated and manageable. In this article, we’ll explore how to create new lists for each iteration.
Using List Comprehension
List comprehension is an efficient and concise way to generate a new list in each iteration of a loop. It is particularly useful when the logic for list creation is straightforward.
Python
a = [1, 2, 3, 4]
res = []
for n in a:
new_list = [n * i for i in range(1, 4)] # Multiplying by 1, 2, and 3
res.append(new_list)
print(res)
Output[[1, 2, 3], [2, 4, 6], [3, 6, 9], [4, 8, 12]]
Explanation:
- The new list is created dynamically for each iteration using
[n * i for i in range(1, 4)]
. - List comprehension reduces the lines of code while improving readability.
Let's explore some more methods for creating a new list for each for loop.
Using map()
map()
function allows us to apply a transformation to all elements in an iterable, generating lists efficiently.
Python
a = [1, 2, 3, 4]
res = list(map(lambda n: [n * i for i in range(1, 4)], a))
print(res)
Output[[1, 2, 3], [2, 4, 6], [3, 6, 9], [4, 8, 12]]
Explanation:
map()
function applies a lambda function to each element of the numbers
list.- This approach minimizes code length by combining mapping and list comprehension.
Using a Function Inside the Loop
Encapsulating the logic in a function makes the code reusable and modular.
Python
def generate_list(n):
return [n * i for i in range(1, 4)]
a = [1, 2, 3, 4]
res = []
for n in a:
new_list = generate_list(n)
res.append(new_list)
print(res)
Output[[1, 2, 3], [2, 4, 6], [3, 6, 9], [4, 8, 12]]
Explanation:
- Here, the
generate_list()
function simplifies the loop by centralizing the list creation logic. - Separating functionality into a function makes the code easier to extend.
Using Nested Loops
Nested loops allow more flexibility, especially when generating lists that depend on multiple variables or ranges.
Python
outer = [1, 2, 3]
res = []
for o in outer:
new_list = []
for i in range(1, 4):
new_list.append(o * i)
res.append(new_list)
print(res)
Output[[1, 2, 3], [2, 4, 6], [3, 6, 9]]
Explanation:
- The inner loop creates a list by appending values one by one.
- The outer loop resets the
new_list
in each iteration.
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