(Python) How can I convert a list of integers into a list of sets where each set is a pair of these integers?

Question

I have a list E = [1,2,3,4,5,6,7,8] and I will like to convert it into E = [{1,2}, {3,4}, {5,6}, {7,8}] in the least computationally expensive manner. In particular, I will like to extend this to large instances of E.

Is there an efficient way to do this in Python (3.5 & later)?

Remark: E will always be given as an even-sized list, as I am working on graphs related topics

Is the list always going to be an even number of elements? – LinkBerest Aug 19 '18 at 03:40 — LinkBerest, Aug 19 '18 at 03:40
@JGreenwell Yes it is. I'll update my question accordingly. – Stoner Aug 19 '18 at 03:41 — Stoner, Aug 19 '18 at 03:41

score 3 · Accepted Answer · answered Aug 19 '18 at 03:32

3

I believe the best method would be using iter+zip in a list comprehension

s = iter(E)
[{a,b} for a,b in zip(s,s)]

Explanation: zip(s,s) performs a pretty efficient pairwise grouping of E if s is its iter.

answered Aug 19 '18 at 03:32

rafaelc

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Only if the list is evenly sized. – cs95 Aug 19 '18 at 03:37
@coldspeed thanks for the comment! If not evenly sized, have to add manually the last item – rafaelc Aug 19 '18 at 03:41
1

Thanks for the explanation! I tried it on large instances of E (in the thousands), and it runs pretty fast :) – Stoner Aug 19 '18 at 03:49

score 2 · Answer 2 · answered Aug 19 '18 at 03:43

2

You can iterate over a rolling slice of 2 of E:

[set(E[i:i+2]) for i in range(0, len(E), 2)]

Note that this works for odd-sized lists as well.

answered Aug 19 '18 at 03:43

blhsing

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Thanks for the feedback! I'll accept @RafaelC's answer as it runs somewhat faster than your implementation. P.S. Ran out of up votes for the day, somehow :/ – Stoner Aug 19 '18 at 03:50

score 1 · Answer 3 · answered Aug 19 '18 at 03:36

1

You can also use zip() plus slicing:

[{x, y} for x, y in zip(E[::2], E[1::2])]

answered Aug 19 '18 at 03:36

RoadRunner

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(Python) How can I convert a list of integers into a list of sets where each set is a pair of these integers?

3 Answers3