Python | Ways to flatten a 2D list
Given a 2D list, write a Python program to convert the given list into a flattened list.
Method #1: Using chain.iterable()
Python3
# Python code to demonstrate# converting 2d list into 1d list# using chain.from_iterables# import chainfrom itertools import chainini_list = [[1, 2, 3], [3, 6, 7], [7, 5, 4]] # printing initial listprint ("initial list ", str(ini_list))# converting 2d list into 1d# using chain.from_iterablesflatten_list = list(chain.from_iterable(ini_list))# printing flatten_listprint ("final_result", str(flatten_list)) |
Output:
initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method #2: Using list comprehension
Python3
# Python code to demonstrate# converting 2d list into 1d list# using list comprehension# import chainfrom itertools import chainini_list = [[1, 2, 3], [3, 6, 7], [7, 5, 4]] # printing initial listprint ("initial list ", str(ini_list))# converting 2d list into 1d# using list comprehensionflatten_list = [j for sub in ini_list for j in sub]# printing flatten_listprint ("final_result", str(flatten_list)) |
Output:
initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method #3: Using functools.reduce
Python3
# Python code to demonstrate# converting 2d list into 1d list# using functools.reduce# import functoolsfrom functools import reduceini_list = [[1, 2, 3], [3, 6, 7], [7, 5, 4]] # printing initial listprint ("initial list ", str(ini_list))# converting 2d list into 1d# using functools.reduceflatten_list = reduce(lambda z, y :z + y, ini_list)# printing flatten_listprint ("final_result", str(flatten_list)) |
Output:
initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method #4: Using sum
sum has an optional argument: sum(iterable [, start])
Python3
# Python code to demonstrate# converting 2d list into 1d list# using sumini_list = [[1, 2, 3], [3, 6, 7], [7, 5, 4]]# printing initial listprint ("initial list ", str(ini_list))# converting 2d list into 1dflatten_list = sum(ini_list, [])# printing flatten_listprint ("final_result", str(flatten_list))# This code is contributed by# Mayank Chaudhary - chaudhary_19 |
Output:
initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method #5: Using lambda
Python3
#Python 3 code to flatten nested list#contributed by S Lakshman Rao - kaapalxini_list=[[1, 2, 3], [3, 6, 7], [7, 5, 4]]#Using lambdaflatten_list = lambda y:[x for a in y for x in flatten_list(a)] if type(y) is list else [y]print("Initial list ",ini_list) #printing initial listprint("Flattened List ",flatten_list(ini_list)) # printing flattened list |
Output:
Initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] Flattened List [1, 2, 3, 3, 6, 7, 7, 5, 4]
Method #6: Using numpy
Python3
#Python 3 code to flatten nested list#Contributed by S Lakshman Rao - kaapalximport numpyini_list=[[1, 2, 3], [3, 6, 7], [7 ,5, 4]]print("Initial list ",ini_list) #Printing Initial listprint("Flattened List ",list(numpy.concatenate(ini_list).flat))#Using numpy to flatten list and printing the result |
Output:
Initial list [[1, 2, 3], [3, 6, 7], [7, 5, 4]] Flattened List [1, 2, 3, 3, 6, 7, 7, 5, 4]
