CODEWITHSUNDEEP
pythonlistcircular-listpairwise
Rubens Benevides
Rubens Benevides

Reputation: 153

How to create a circular list in one line of code?

Given the following list:

labels = [0, 1, 2, 3, 4]

I wish I could obtain the following by using just one line of code:

['0-1', '1-2', '2-3', '3-4', '4-0']

I can do this with 2 lines of code:

pairwise_labels = [f"{i}-{i+1}" for i in range(len(labels)-1)]
pairwise_labels.append(f"{len(labels)-1}-0")

With just one line, my code will be drastically reduced, as I always need to create an if for the last case to close the loop.

Upvotes: -1

Views: 129

Answers (5)

Alain T.
Alain T.

Reputation: 42133

You can leverage Python's ability to use negative indexes:

labels = [0, 1, 2, 3, 4]

pl = [f"{a}-{labels[i]}" for i,a in enumerate(labels,1-len(labels))]

print(pl)

['0-1', '1-2', '2-3', '3-4', '4-0']

Upvotes: 1

Corralien
Corralien

Reputation: 120509

You can slice your list:

>>> [f'{i}-{j}' for i, j in zip(labels, labels[1:] + labels[:1])]

['0-1', '1-2', '2-3', '3-4', '4-0']

Upvotes: 2

Luca Anzalone
Luca Anzalone

Reputation: 749

Your one liner:

pairwise_labels = [f'{a}-{b}' for a, b in zip(labels, labels[1:] + [labels[0]])]

Upvotes: 2

Timeless
Timeless

Reputation: 37847

One option would be to use pairwise (New in version 3.10) :

from itertools import pairwise

labels = [0, 1, 2, 3, 4]

pairwise_labels = [f"{x}-{y}" for x, y in pairwise(labels + [labels[0]])]

Output :

print(pairwise_labels)

#['0-1', '1-2', '2-3', '3-4', '4-0']

Upvotes: 4

Huzaifa Zahoor
Huzaifa Zahoor

Reputation: 335

You can do this in one line using modular arithmetic.

pairwise_labels = [f"{labels[i]}-{labels[(i+1)%len(labels)]}" for i in range(len(labels))]

Upvotes: 3

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