Python - Convert list of string to list of list

In Python, we often encounter scenarios where we might have a list of strings where each string represents a series of comma-separated values, and we want to break these strings into smaller, more manageable lists. In this article, we will explore multiple methods to achieve this.

Using List Comprehension

List comprehension is a concise way to create lists. By combining it with the split() method, which splits a string into a list based on a specified delimiter, we can efficiently transform a list of strings into a list of lists.

a = ["GeeksforGeeks"]

result = [item.split(",") for item in a]
print(result)

[['GeeksforGeeks']]

Explanation:

• The split(",") method is applied to each string in the list, splitting it wherever a comma appears.
• The list comprehension iterates over each string (item) in the list and applies the split() method.
• The result is a new list, where each string has been converted into a list of substrings.

Let's explore some more methods and see how we can convert a list of strings to a list of lists.

Using map() with split()

map() function applies a specified function to each item in an iterable. When combined with the split() method, it can be used to transform a list of strings into a list of lists.

a = ["Learn,Python,with,Gfg", "GeeksforGeeks"]

res = list(map(lambda x: x.split(","), a))
print(res)

[['Learn', 'Python', 'with', 'Gfg'], ['GeeksforGeeks']]

Explanation:

• The map() function takes two arguments: a function (in this case, a lambda function that applies split(",")) and an iterable (the list).
• Each string in the data list is processed by the split() method, producing a list of substrings.
• The list() function converts the result of map() into a list.

Using a for Loop

Using a traditional for loop in Python is a simple way to achieve the conversion.

a = ["Learn,Python,with,GFG", "GeeksforGeeks"]

res = []
for item in a:
    res.append(item.split(","))
print(res)

[['Learn', 'Python', 'with', 'GFG'], ['GeeksforGeeks']]

Explanation:

• An empty list result is initialized to store the transformed data.
• The for loop iterates over each string (item) in the list.
• The split(",") method is applied to each string, and the resulting list is appended to the result list.

Using Regular Expressions with re.split()

If the delimiter is more complex (e.g., multiple delimiters or patterns), regular expressions provide a powerful alternative. The re.split() function can split strings based on patterns rather than fixed delimiters.

import re

a = ["Learn|Python|with|GFG", "Geeks|for|Geeks"]

res = [re.split(r"\|", item) for item in a]
print(res)

[['Learn', 'Python', 'with', 'GFG'], ['Geeks', 'for', 'Geeks']]

Explanation:

• The re.split() function splits strings based on a regular expression pattern. Here, the pattern r"\|" matches the pipe (|) character.
• List comprehension is used to apply re.split() to each string in the data list.
• The result is a list of lists where each string is split based on the specified pattern.