Python Flatten Array of Arrays

Sometimes we work with arrays (lists) that contains arrays (lists). In order to make some manipulations or simply readability, we need to transform this array of arrays into a flat one. In this tutorial, we will learn different methods to flatten an array of arrays with Python.

Method 1: Nested for loop

We can iterate over each element of the outer array and, inside this loop, iterate over each element of the inner array. Then, we append each element to a new flat list.

def flatten(arr):
    flat_arr = []
    for sublist in arr:
        for ele in sublist:
            flat_arr.append(ele)
    return flat_arr

Method 2: List comprehension

We can use a nested list comprehension to flatten an array of arrays. In this method, we iterate over each element of each sublist, and append it to a new flat list.

def flatten(arr):
    flat_arr = [ele for sublist in arr for ele in sublist]
    return flat_arr

Method 3: itertools.chain

We can use the itertools.chain function to chain all the sublists into one flat list.

import itertools

def flatten(arr):
    flat_arr = list(itertools.chain.from_iterable(arr))
    return flat_arr

Method 4: Recursive function

We can define a recursive function that flattens any arbitrary nested list. In this function, we check if an element is a list. If it is, we call the function again passing this element as a parameter. If it is not, we append this element to a new flat list.

def flatten(arr):
    flat_arr = []
    for ele in arr:
        if isinstance(ele, list):
            flat_arr.extend(flatten(ele))
        else:
            flat_arr.append(ele)
    return flat_arr

Conclusion

In this tutorial, we saw different methods to flatten an array of arrays with Python. Depending on the situation, we should choose the most efficient and readable method for our code.