Python | Convert given list into nested list
Last Updated :
07 Dec, 2023
Sometimes, we come across data that is in string format in a list and it is required to convert it into a list of the list. This kind of problem of converting a list of strings to a nested list is quite common in web development. Let’s discuss certain ways in which this can be performed.
Convert the Given List into Nested List in Python
Below are the ways by which we can convert a given list into a Nested List in Python:
- Using iteration
- Using a list with numeric values
- Using map(), split() and lambda
- Using list comprehension
- Using numpy library
- Using heapq
Convert the Given List into Nested List Using Iteration
In this example, the Python code takes a list of strings, where each string contains comma-separated values, and converts it into a list of lists. It achieves this by first splitting each string into individual elements and then organizing them into sublists, resulting in the desired list of lists named “Output”.
Python3
Input = ['Geeeks, Forgeeks', '65.7492, 62.5405',
'Geeks, 123', '555.7492, 152.5406']
temp = []
for elem in Input:
temp2 = elem.split(', ')
temp.append((temp2))
Output = []
for elem in temp:
temp3 = []
for elem2 in elem:
temp3.append(elem2)
Output.append(temp3)
print(Output)
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Output
[['Geeeks', 'Forgeeks'], ['65.7492', '62.5405'], ['Geeks', '123'], ['555.7492', '152.5406']]
Python Convert List into Nested List Using List With Numeric Values
In this example, the Python code utilizes the ast.literal_eval function to safely convert a list of comma-separated string elements (Input) into a list of lists (Output) containing numerical values, demonstrating an approach that ensures proper evaluation and avoids potential security risks.
Python3
import ast
Input = ['12, 454', '15.72, 82.85', '52.236, 25256', '95.9492, 72.906']
Output = [list(ast.literal_eval(x)) for x in Input]
print(Output)
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Output
[[12, 454], [15.72, 82.85], [52.236, 25256], [95.9492, 72.906]]
Time complexity: O(n), where n is the length of the input list Input.
Auxiliary space: O(n), where n is the length of the input list Input.
Convert Python List into Nested List Using map(), split() and lambda
We use the map function to apply a function (in this case, the split function) to each element in a list (in this case, the list of strings). The map function returns an iterator that applies the function to each element of the list, and returns the results as a new iterator. To obtain the final result as a list, we use the list function to convert the iterator returned by map into a list.
Python3
Input = ['Geeeks, Forgeeks', '65.7492, 62.5405',
'Geeks, 123', '555.7492, 152.5406']
Output = list(map(lambda x: x.split(', '), Input))
print("Result: "+str(Output))
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Output
Result: [['Geeeks', 'Forgeeks'], ['65.7492', '62.5405'], ['Geeks', '123'], ['555.7492', '152.5406']]
Time complexity: O(n)
Auxiliary Space: O(n)
Turning a List into Nested Lists in Python Using List Comprehension
The program converts a list of strings into a list of lists by splitting each string by a comma followed by a space. In this example, the Python code initializes a list of strings (Input) with comma-separated values. It employs list comprehension to split each string into elements and create a list of lists (output). The result is then printed, showcasing a concise approach for transforming the input strings into organized sublists.
Python3
Input = ['Geeeks, Forgeeks', '65.7492, 62.5405',
'Geeks, 123', '555.7492, 152.5406']
output = [elem.split(', ') for elem in Input]
print(output)
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Output
[['Geeeks', 'Forgeeks'], ['65.7492', '62.5405'], ['Geeks', '123'], ['555.7492', '152.5406']]
Time complexity: O(n), where n is the number of strings in Input.
Auxiliary Space: O(n), because the resulting list output has n sublists, each containing two elements.
Python Convert List into Nested List Using numpy
In this example, the Python code leverages NumPy to transform a list of strings (Input) with comma-separated values into a NumPy array (output). The array is created using list comprehension and then converted back to a nested list for printing.
Python3
import numpy as np
Input = ['Geeeks, Forgeeks', '65.7492, 62.5405',
'Geeks, 123', '555.7492, 152.5406']
output = np.array([elem.split(', ') for elem in Input])
print(output.tolist())
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Output:
[['Geeeks', 'Forgeeks'], ['65.7492', '62.5405'], ['Geeks', '123'], ['555.7492', '152.5406']]
Time complexity: O(n)
Auxiliary Space: O(n)
Python Turning a List into Nested Lists Using heapq
In this example, the Python code utilizes the heapq module to create a min-heap (output) of lists resulting from splitting strings in a list (Input) with comma-separated values. The min-heap is then popped to retrieve the elements in ascending order, demonstrating the use of heaps for ordered processing.
Python3
import heapq
Input = ['Geeeks, Forgeeks', '65.7492, 62.5405',
'Geeks, 123', '555.7492, 152.5406']
output = []
for elem in Input:
heapq.heappush(output, elem.split(', '))
output = [heapq.heappop(output) for i in range(len(output))]
print(output)
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Output
[['555.7492', '152.5406'], ['65.7492', '62.5405'], ['Geeeks', 'Forgeeks'], ['Geeks', '123']]
Time complexity: O(n log n)
Auxiliary Space: O(n)
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