First clear solution for Non-unique Elements by Renelvon - python coding challenges

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First solution in Clear category for Non-unique Elements by Renelvon

from collections import Counter

def checkio(data):
    count = Counter(data)
    count.subtract(set(data))
    return [x for x in data if x in +count]

#These "asserts" using only for self-checking and not necessary for auto-testing
if __name__ == "__main__":
    assert isinstance(checkio([1]), list), "The result must be a list"
    assert checkio([1, 2, 3, 1, 3]) == [1, 3, 1, 3], "1st example"
    assert checkio([1, 2, 3, 4, 5]) == [], "2nd example"
    assert checkio([5, 5, 5, 5, 5]) == [5, 5, 5, 5, 5], "3rd example"
    assert checkio([10, 9, 10, 10, 9, 8]) == [10, 9, 10, 10, 9], "4th example"

Feb. 11, 2014

Comments:

bryukh on Feb. 14, 2014, 5:48 a.m.
Interesting. But for the "clear" category you can add some comments (for newbies).

Renelvon on Feb. 22, 2014, 1:42 p.m.
Perhaps I could get rid of the 'subtract' and just use <pre class='brush: python'>return [x for x in data if count[x] > 1] </pre> This would have been simpler but the solution is meant to showcase collections.Counter and some of its (intuitive?) functionality. Apart from a suggestion to read the relevant documentation, what kind of comment would make the code clearer?

TomoyaKikuno on Feb. 15, 2014, 10:36 a.m.
It is simple and interesting.

jiahe.lim.1 on July 8, 2014, 2:28 p.m.
What does the + in +count do? in <pre class='brush: python'> return [x for x in data if x in +count] </pre> Does anyone know? Been reading up on list comprehension but can't seem to find any mention of such usage. Much appreciated!

Renelvon on July 8, 2014, 10:18 p.m.
This has nothing to do with list comprehensions. When applying a unary plus to a Counter object, another such object is produced which contains only those elements with positive counts. See the documentation. <a href="https://docs.python.org/dev/library/collections.html">https://docs.python.org/dev/library/collections.html</a>#collections.Counter

jiahe.lim.1 on July 9, 2014, 12:30 a.m.
Thank you! Looks like I was looking in the wrong place! Much appreciated!

mailsiraj on Jan. 20, 2020, 4:58 a.m.
Wow - what a wonderful solution, but being new to python, it took me a lot of time to understand what is going on. I entered the following code into Jupyter and stepped through it one by one to get an idea - beautiful code. Adding comment to each line so that beginners like me would understand would be much appreciated. <pre class='brush: python'>data = [1, 2, 3, 1, 3] from collections import Counter count = Counter(data) count </pre> <blockquote> Counter({1: 2, 2: 1, 3: 2}) </blockquote> <pre class='brush: python'>set(data) </pre> <blockquote> {1, 2, 3} </blockquote> <pre class='brush: python'>count.subtract(set(data)) count </pre> <blockquote> Counter({1: 1, 2: 0, 3: 1}) </blockquote> <pre class='brush: python'>+count </pre> <blockquote> Counter({1: 1, 3: 1}) </blockquote> <pre class='brush: python'>[x for x in data if x in +count] </pre> <blockquote> [1, 3, 1, 3] </blockquote>

ithink2020_01e0c5f00e1e4e2eb88 on March 25, 2021, 12:53 p.m.
Thank you for this!

BlindB on April 13, 2021, 1:13 p.m.
Cool! This plus in comprehension force me to thoroughly read collections.Counter in docs.

Aleksandr_Kazakov on July 21, 2023, 1:12 p.m.
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