The Key clear solution for Absolute Sorting by bryukh - python coding challenges

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The Key solution in Clear category for Absolute Sorting by bryukh

def checkio(numbers_array):
    """
    The magic of the key :)
    """
    return tuple(sorted(numbers_array, key=abs))

Feb. 20, 2014

Comments:

casilda on Feb. 20, 2014, 8:55 p.m.
Cool! I didn't realise you could use a key without arguments. So the function you specify as a key is automatically applied to all items in the sorted iterable here? Can you do this with any built-in function that would normally require an explicit argument?

bryukh on Feb. 20, 2014, 11:08 p.m.
Yes and yes. I placed the links in the task description about it.

casilda on Feb. 20, 2014, 11:57 p.m.
Thanks!

EthyBOX on Jan. 27, 2015, 3:31 p.m.
Clever use of key, thanks!

veky on July 26, 2015, 7:22 p.m.
Not only builtin function. Any callable can go there. <pre class='brush: python'>class BySign(int): def __lt__(self, other): x, y = map(int, (self, other)) return 0 <= x < y or y < x < 0 or x < 0 < y >>> sorted([5, -2, 3, -8, 1, 0, 3], key=BySign) [-2, -8, 0, 1, 3, 3, 5] </pre> <hr /> Function "requires an explicit argument" only if you intend to call it. The same way a number "requires an explicit factor" only if you intend to multiply it. :-) It can stand on its own, and be passed to other functions, without any problem. <pre class='brush: python'>>>> id(abs), type(abs), repr(abs) (3546784, <class 'builtin_function_or_method'>, '<built-in function abs>') >>> *map(abs, [3, -5, -2, 0]), (3, 5, 2, 0) </pre> You can also <pre class='brush: python'>print(abs), dir(abs), hash(abs), help(abs) </pre> or you can even get attributes: <pre class='brush: python'>abs.__name__, abs.__doc__, abs.__self__, abs.__text_signature__ </pre> Moreover, you can do that (or similar) with any object. The only thing callables are special about, is that they have an attribute `call`. <pre class='brush: python'>>>> hasattr(abs, '__call__') True >>> abs.__call__(-5) 5 </pre>

yang.wang04 on June 2, 2016, 2:23 a.m.
It is clear to me. Thanks a lot.

Amachua on Feb. 21, 2014, 10:35 a.m.
Python 3.x way :) P.S. Why use tuple here? It works fine without it :)

bryukh on Feb. 21, 2014, 11:06 p.m.
"The list or tuple" I had tossed a coin and chose the tuple :-)

Cjkjvfnby on March 2, 2014, 9:58 p.m.
Simple is better than complex.

bryukh on March 2, 2014, 10:30 p.m.
The coin does not think so ;-)

Cjkjvfnby on March 3, 2014, 6:55 a.m.
Then you need to use coinsort instead of Timsort :)

ArchTauruS on June 22, 2014, 3:51 p.m.
bla bla

leggewie on June 13, 2021, 9:17 a.m.
but there is no need for the coin toss, as <a href="https://py.checkio.org/mission/absolute-sorting/publications/leggewie/python-3/second-straight-forward-use-of-key/">neither tuple nor list are necessary</a>... Python2 vs. Python3 or something of that nature?

artemrudenko on Feb. 21, 2014, 11:07 a.m.
Magic is always around us

Cjkjvfnby on March 2, 2014, 9:57 p.m.
There is function has_magic inside glob module :)

veky on July 26, 2015, 7:25 p.m.
<a href="https://hg.python.org/cpython/file/3.5/Lib/glob.py#l128">Indeed</a>. :-)

Reb_Sadran on March 20, 2014, 8:10 a.m.
took me 30 minutes of googling and playing with keys to find out that key can actually be used without arguments.

veky on Nov. 9, 2015, 8:54 a.m.
Aaargh. I'm always incredibly sad when I see such posts. Google "Python sort". Feel lucky. Click on "Key functions". Get to <a href="https://wiki.python.org/moin/HowTo/Sorting#Key_Functions">this link</a>. See first example. Why is that so hard? I'm not ranting, I'm genuinely curious. Where do you people spend those 30 minutes??

veky on July 4, 2017, 4:35 a.m.
I'm not really sad, but I'm perplexed when people who obviously like me and "could read my posts the whole day", come here and just -1 this post. Yes, I know I lack tact. No, -1 won't help much. But I'm also in a position to profit greatly from an insight into that question. I teach a course at university, and at the exam, students need to write some 30 lines of Python. Concerning the area they know in advance will be on an exam. Most of the lines are "business as usual", and some of them are tricky. Of course, you don't have to write everything if you just want to pass. And they do write them (mostly:). It's not that they don't know. It's just that they take three hours to do it! And they still complain they didn't have enough time. I have halved the amount of programming they have to do, and given them 50% more time, but it's still the same. It seems to me that if I give them the whole week, they'd still write their program the whole time. My only theory is that for many students, time passes at a different rate when they are solving programming problems. :-D -1 is not really relevant. But I'd give a 1000 points of my reputation here just to gain insight into this phenomenon.

leggewie on June 13, 2021, 9:14 a.m.
I think the answer has at least two components. <ul> <li>talent (to think like a computer)</li> <li>experience</li> </ul> and yes, you have both and have apparently lost another skill which is compassion to understand the reality of others who haven't quite reached your level of skill in those two areas. I can certainly very much feel for those who take 30 minutes or even a whole day to solve a problem that others can jot down in 30 seconds without even thinking. I'm still there. Most likely, you were there once, too.

veky on June 13, 2021, 10:18 a.m.
Everything I can agree with, only I wouldn't say I lost compassion. There is strong evidence I never had it. :-| I'd even say that with time I just learned how to fake it better, since sometimes it's necessary for functioning in the society (fortunately not on CiO, which is why I like being here:). But yes, compassion (empathy?) would probably help. Anyway, thank you for the answer, but it doesn't help me much. Their talent I can probably never influence, but maybe I can level up their experience, if only "faked" one, by spending more time preparing and solving similar tasks.

fokadog on March 27, 2014, 5:29 p.m.
...

MarkVickers on Nov. 10, 2014, 10:47 p.m.
Excellent. Aside from the links in the task description, are there other good sources of information on the use of keys in this way?

donBit on Nov. 11, 2014, 9:07 p.m.
This are the kind of things that I gonna tell others when ask me about why is a good idea to learn python, awesome challenge thanks !!

greenit on Dec. 11, 2014, 8:31 a.m.
Lookes like mine (except I didn't use tuple). ;-)

giolefpaceid on Feb. 20, 2015, 10:49 p.m.
Nice one! Similar solution here!

bryukh on Feb. 21, 2015, 1:09 p.m.
thx

Sterncat on March 14, 2015, 6:22 a.m.
Wooo! That's so cool!!!!! I love python even more!

saikat_dutta779 on May 31, 2015, 1:46 p.m.
Can you lend me your brain bro? :) :P

bryukh on June 10, 2015, 5:15 a.m.
Sorry, only one in my head :-)

xiaomutoun on June 12, 2015, 3:30 p.m.
Hello, I didn't add "tuple()" on the result of sorted(), and it pass.

vinegret on July 2, 2015, 12:24 p.m.
similarly

szymcio2001 on June 14, 2015, 9:07 a.m.
Absolutely perfect.

fh2game86 on July 31, 2015, 12:41 a.m.
return sorted(numbers_array, key=abs) , why tuple ???

bryukh on Aug. 3, 2015, 7:39 a.m.
You don't like tuples? ;-)

fh2game86 on Aug. 3, 2015, 10:38 p.m.
:) no no i don't think that way , it's because it don't need a tuple.

bryukh on Aug. 4, 2015, 5:52 a.m.
Honestly in first version we had used tuple type checking of results, then we removed it, but "tuple" conversion are remained.

texom512 on Aug. 15, 2015, 3:17 p.m.
tuple() isn't necessary.

shuai on Oct. 3, 2015, 2:27 a.m.
why tuple()?

M157q on Nov. 5, 2015, 4:06 p.m.
same as mine. simple and elegant. thanks to the key. lol

ducthinhdt on Nov. 14, 2015, 3:53 a.m.
Elegant solution

andriiabaimov on Dec. 7, 2015, 3:46 p.m.
The only right solution, very clear.

ljy95135 on May 26, 2016, 10:20 a.m.
I use a <pre class='brush: python'>key=lambda x:abs(x) </pre> now I find I am quite wrong... Good answer!

veky on June 2, 2016, 4:50 a.m.
That's not wrong, that's just needlessly complicating things. Same as <pre class='brush: python'>if x > 5: return True else: return False </pre> :-)

ljy95135 on June 2, 2016, 5:16 a.m.
Yes, so modifying is important, to make a right one better. :-)

Sora-Shiro on Oct. 15, 2016, 3:24 p.m.
Almost the same as mine!But I use math.fabs so I have to add import math, which increases a line in my code. By the way, as a beginner, I learned a lot from your and others` code this week.Checkio is funny, I like it!

davejlin on Nov. 30, 2016, 3:18 p.m.
awesome! i also used the key, except i went through the trouble of embedding abs in a lambda function. forgot that i could apply abs directly, lol. thanks! <pre class='brush: python'>sorted(numbers_array, key=lambda x: abs(x)) </pre>

porosya on June 30, 2018, 1:59 a.m.
IMHO tuple is not necessary

channeldsrphone on Oct. 5, 2018, 10:53 p.m.
WTF! I think, that I can't also sort this tuple! I do this shit arrB = sorted([abs(i) for i in arrA], key=abs) for i in arrB: if (-i) in arrA: arrB = arrB[:arrB.index(i)] + [-i] + arrB[arrB.index(i)+1:]

Joe_Salmans on March 29, 2019, 11:30 p.m.
Cool. The lambda function I used was apparently unnecessary!

lifeshow30s on July 8, 2020, 3:35 p.m.
if I want to apply a method as a key, how could I write the code? let's take sorting by lowercase for example. <pre class='brush: python'>a = ['a', 'A', 'c', 'D', 'e', 'G'] sorted(a, key = str.lower) </pre> why we use str not other name? is str an atrribute or something?

veky on Aug. 13, 2020, 3:19 p.m.
No, str is a class. <pre class='brush: python'>>>> type('') is str True </pre> When x is an instance of a class X, then x.method(y,z) is (usually) the same as X.method(x,y,z). That is, method is looked up in the namespace of x's type, and then supplied x in front of other parameters (usually named self inside method). So, x.lower(), when x is a str, is the same as str.lower(x). Also, ''.join(something) is the same as str.join('', something).

space_geol on Oct. 9, 2020, 5:55 a.m.
Never knew you could use key that way!

Zeonz on Nov. 30, 2022, 7:21 p.m.
Well you just made me learn how the key function works, and I was looking for something like the abs() function. So... Thank you.

lisovsky on Jan. 7, 2023, 11:09 a.m.
tuple() isn’t necessary.

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