Consider the below list of lists:
my_list = [[1,2], [3,4], ['a', 'b'], [1.23, 5.73]]
What if you wish to flatten this list, i.e get all the elements in a single list rather than have multiple lists inside a master list?
This can be done in various ways in python, and we will cover a few of them in this post.
1. Using a new list
The below method creates a new list, and the old list of lists is iterated through and every element present in the list of lists is appended to the new list.
my_list = [[1,2], ['abc', 'studytonight'], ['a', 'b'], [1.23, 5.73]]
flat_list = []
for sublist in my_list:
for item in sublist:
flat_list.append(item)
print(flat_list)
Output:
[1, 2, 'abc', 'studytonight', 'a', 'b', 1.23, 5.73]
2. Using list comprehension
List comprehension can be used to flatten a list of lists. It has been demonstrated below:
my_list = [[1,2], ['abc', 'studytonight'], ['a', 'b'], [1.23, 5.73]]
flat_list = [item for sublist in my_list for item in sublist]
print(flat_list)
Output:
[1, 2, 'abc', 'studytonight', 'a', 'b', 1.23, 5.73]
3. Using the iterable method from the itertools module
import itertools
my_list = [[1,2], ['abc', 'studytonight'], ['a', 'b'], [1.23, 5.73]]
flat_list = list(itertools.chain.from_iterable(my_list))
print(flat_list)
Output:
[1, 2, 'abc', 'studytonight', 'a', 'b', 1.23, 5.73]
4. Using the concat method from functools
import functools
my_list = [[1,2], ['abc', 'studytonight'], ['a', 'b'], [1.23, 5.73]]
functools.reduce(operator.concat, my_list)
Output:
[1, 2, 'abc', 'studytonight', 'a', 'b', 1.23, 5.73]
Note: Instead of the concat method in the above code, iconcat method also can be used. It flattens the list of lists and gives the same output as that of using the concat method.
5. Using the numpy module's flat option
If you are new to numpy, here is an introduction to Numpy for beginners.
import numpy
my_list = [[1,2], ['abc', 'studytonight'], ['a', 'b'], [1.23, 5.73]]
list(numpy.array(my_list).flat)
Output:
['1', '2', 'abc', 'studytonight', 'a', 'b', '1.23', '5.73']
6. Using the concatenate method from the numpy module
import numpy
my_list = [[1,2], ['abc', 'studytonight'], ['a', 'b'], [1.23, 5.73]]
list(numpy.concatenate(my_list))
Output:
['1', '2', 'abc', 'studytonight', 'a', 'b', '1.23', '5.73']
7. Using the reduce method
from functools import reduce
my_list = [[1,2], ['abc', 'studytonight'], ['a', 'b'], [1.23, 5.73]]
reduce(lambda x,y: x+y, my_list)
Output:
[1, 2, 'abc', 'studytonight', 'a', 'b', 1.23, 5.73]
8. Using the iterable method from the collections module
my_list = [[1,2], ['abc', 'studytonight'], ['a', 'b'], [1.23, 5.73]]
from collections import Iterable
def flatten(items):
for x in items:
if isinstance(x, Iterable) and not isinstance(x, (str, bytes)):
yield from flatten(x)
else:
yield x
list(flatten(my_list))
Output:
[1, 2, 'abc', 'studytonight', 'a', 'b', 1.23, 5.73]
Conclusion
In this post, we saw different ways in which a list of a list can be flattened. Do let us know whether you have a different approach to it.
