Unique single values from list of tuple pairs?

Question

From this data structure: [(1,2),(1,3),(1,4),(1,5)] I am tying to get the unique values, or [1,2,3,4,5]. What's the easy solution here?

Is using an intermediate set ok? – Nic Feb 05 '17 at 23:18 — Nic, Feb 05 '17 at 23:18

score 5 · Accepted Answer · answered Feb 05 '17 at 23:18

5

You can use set with list comprehension:

lst = [(1,2),(1,3),(1,4),(1,5)]

set(j for i in lst for j in i)
# {1, 2, 3, 4, 5}

answered Feb 05 '17 at 23:18

Psidom

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This is the first and most easy/pythonic way to solve the question. Great answer. – Chiheb Nexus Feb 06 '17 at 00:03
2

You could also use a set-comprehension: `{j for i in lst for j in i}`. :) – MSeifert Feb 06 '17 at 00:38

score 2 · Answer 2 · edited May 23 '17 at 12:17

Use chain.from_iterable from the itertools module. It's generally considered to be the idiomatic way to flatten a 2D iterable as opposed to a nested list comprehension. See this question.

>>> from itertools import chain
>>> set(chain.from_iterable([(1,2),(1,3),(1,4),(1,5)]))
{1, 2, 3, 4, 5}

chain.from_iterable flattens the list and set keeps only unique values.

To convert back to a list, simply pass to the list constructor.

>>>list(set(chain.from_iterable([(1,2),(1,3),(1,4),(1,5)])))
[1, 2, 3, 4, 5]

score 0 · Answer 3 · answered Feb 06 '17 at 00:37

In your expected output the order of the unique elements follows the order of appearance. One way to do it would be (using an external library but the recipes are avaiable in the itertools-recipes section):

>>> from iteration_utilities import flatten, unique_everseen

>>> x = [(1,2),(1,3),(1,4),(1,5)]

>>> list(unique_everseen(flatten(x)))
[1, 2, 3, 4, 5]

Unique single values from list of tuple pairs?

3 Answers3