Flatten tuple of List to tuple - Python

The task of flattening a tuple of lists to a tuple in Python involves extracting and combining elements from multiple lists within a tuple into a single flattened tuple. For example, given tup = ([5, 6], [6, 7, 8, 9], [3]), the goal is to flatten it into (5, 6, 6, 7, 8, 9, 3).

Using itertools.chain()

This method is a highly efficient to flatten a tuple of lists into a tuple. chain.from_iterable() combines multiple inner lists into a single sequence without creating intermediate lists. It is particularly suitable for large datasets, as it lazily iterates over elements, reducing memory consumption.

from itertools import chain

tup = ([5, 6], [6, 7, 8, 9], [3])

res = tuple(chain.from_iterable(tup))
print(res)

(5, 6, 6, 7, 8, 9, 3)

Explanation: chain.from_iterable(tup) iterates over each sublist inside tup and extracts elements from each sublist in sequence, producing a single continuous stream of elements and tuple() converts this flattened stream into a tuple, creating the final flattened tuple.

Using list comprehension

List comprehension offers a concise approach to flatten a tuple of lists into a single tuple. It unpacks each sublist within the tuple and extracts individual elements into a flat tuple. Though slightly less efficient than itertools.chain() for large datasets, it is still fast and works well for smaller inputs.

tup = ([5, 6], [6, 7, 8, 9], [3])

res = tuple(x for sublist in tup for x in sublist)
print(res)

(5, 6, 6, 7, 8, 9, 3)

Explanation: for sublist in tup iterates through each sublist in tup and for x in sublist iterates over each element x within them. The expression x extracts and flattens all elements into a single sequence and tuple() converts it into the final flattened tuple.

Using sum()

sum() can flatten a tuple of lists by summing the sublists , starting with an empty list. Each concatenation creates a new intermediate list, making it memory-intensive and slow for flattening tuples of lists.

tup = ([5, 6], [6, 7, 8, 9], [3])

res = tuple(sum(tup, []))
print(res)

(5, 6, 6, 7, 8, 9, 3)

Explanation: sum(tup, []) concatenates all sublists in tup into a single list, starting with an empty list [], and tuple() converts the result into a flattened tuple of elements.

Using functools.reduce()

reduce() repeatedly applies a function to combine elements of a tuple of lists into a single flattened list. This functional approach can flatten nested lists, but introduces performance overhead due to function call evaluations. It creates intermediate lists during reductions, making it slower than itertools.chain() and comprehension for flattening tuples of lists.

from functools import reduce
tup = ([5, 6], [6, 7, 8, 9], [3])

res = tuple(reduce(lambda x, y: x + y, tup))
print(res)

(5, 6, 6, 7, 8, 9, 3)

Explanation: reduce(lambda x, y: x + y, tup) combines all sublists in tup by repeatedly concatenating pairs of sublists into a single list and tuple() converts the result into a flattened tuple of elements.