Hinted clear solution for Absolute Sorting by veky - python coding challenges

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Hinted solution in Clear category for Absolute Sorting by veky

checkio=lambda n:sorted(n,key=abs)

Feb. 20, 2014

Comments:

sat0yu on Feb. 22, 2014, 8:02 a.m.
you are a very pythonista!!

veky on Feb. 22, 2014, 10:09 a.m.
Even if I am, you can't conclude it from this. As I said, this was hinted.

mscmorris on Feb. 6, 2015, 5:44 p.m.
Regardless, those of us newer python users who end up with the same solution as you feel pretty good about it :)

veky on Feb. 6, 2015, 7:34 p.m.
You always have <a href="http://www.checkio.org/mission/absolute-sorting/publications/veky/python-3/smn-theorem/?ordering=most_voted">this</a> if you want to push yourself further. ;-)

zlomovsky on Feb. 7, 2015, 4:37 p.m.
I've done <a href="http://www.checkio.org/mission/absolute-sorting/publications/zlomovsky/python-3/very-short/">the same</a>. I just was usung "a" instead of "n". :)

veky on Feb. 7, 2015, 5:03 p.m.
That can also be explained: what is now called "array" was called "numbers" when I solved the task. ;-) Also, see the above comment. ;-)

bryanandrade on July 26, 2015, 2:05 p.m.
Came up with the exact same answer!

veky on July 26, 2015, 6:48 p.m.
Not so surprising. Try <a href="http://www.checkio.org/mission/absolute-sorting/publications/veky/python-3/smn-theorem/?ordering=most_voted">this</a>. ;-)

Czarinov on Aug. 2, 2015, 9:05 a.m.
I kept trying to put key=abs(n) instead of just abs... Had to create [[abs(n),n],...], sort it and extract n. By the way, could you help me: if I have a=[[1,-1],[2,-2]], how do I sort it by the 2nd item (by -1 and -2)?

veky on Aug. 2, 2015, 4:53 p.m.
There are two things to consider here: one, as I said, lambda is just one of the batteries. And it is a bit overused. You can write <pre class='brush: python'>key=lambda n:abs(n) </pre> but `key=abs` is much simpler and more direct. [Formal name is [eta-reduction](<a href="http://www.lambda-bound.com/book/lambdacalc/node21.html).]">http://www.lambda-bound.com/book/lambdacalc/node21.html).]</a> two, the point about "explicit arguments". See <a href="http://www.checkio.org/mission/absolute-sorting/publications/bryukh/python-3/the-key/share/5d3eb4ab50f04b33a3534367eae23572/#comment-33115">this</a>. As I said there, "calling" is just one of many things you can do to a function. Not everything in Python must be an int, str or other "value type" to be transferred somewhere. ((This is closely related to function-value confusion school propagates. Too often teachers speak about "function sin x", making students think that x is somehow a "part" of a function. "sin x" is not a function: it is a complex number if x is a complex number, or an expression if x is a variable. `sin` is a function.)) <hr /> Your technique is well-known, and is called <a href="https://en.wikipedia.org/wiki/Schwartzian_transform">Schwartzian transform</a>. But lately it's not much used, since most normal programming languages support more direct constructs. <blockquote> By the way, could you help me: if I have a=[[1,-1],[2,-2]], how do I sort it by the 2nd item (by -1 and -2)? </blockquote> The true Pythonic way is itemgetter from operator module. <pre class='brush: python'>a.sort(key=itemgetter(1)) </pre> But this is also one of those places where many people just give up and use lambda: <pre class='brush: python'>a.sort(key=lambda item:item[1]) </pre> In Python2, you can use key=reversed. But that's a hack. :-]

Czarinov on Aug. 3, 2015, 11:31 a.m.
Thank you very much, Veky, was of great help ;).

yang.wang04 on June 2, 2016, 2:37 a.m.
sorted([11,20,54,73],key=lambda x:str(x)[1]) How can we use str without lambda in this case?

veky on June 2, 2016, 4:59 a.m.
Depends on what do you actually want to do. I really doubt that you actually want to sort on the second digit. You probably want to sort on the last digit, and that's <pre class='brush: python'>key=10 .__rmod__ </pre> Of course, if you're into pointless programming (that's how pointfree programming is usually called in Python community;), you can first define composition of functions (Guido vehemently forbids adding it to functools stdlib because that would just encourage pointless style:), and use <pre class='brush: python'>key=compose(operator.itemgetter(1), str) </pre> But as I said, that doesn't buy much. I said lambda is overused, not that is shouldn't ever be used. :-)

yang.wang04 on June 14, 2016, 5:51 a.m.
Yes, I actually want to sort on the second digit and just want to get a solution without lambda.Thanks for your solution:)

veky on June 14, 2016, 6:08 a.m.
I must say that in three decades of my life I'm doing programming, from tennis game for a Casio calculator, to a data cleaner and statistical analyzer for a medical database, from direct hardware-manipulating machine language on C64 to a modern core-banking software supporting smart contracts, from automatic tester for students' C++ homework to a symbolic framework for logical deduction, I never had a need to sort a sequence of numbers by their second decimal digit (unless it's also the last digit, as I said). May I ask what's your use case? :-) Of course, if you have a real need for such a specialized function, probably the best thing to do would be <pre class='brush: python'>def second_digit(n: int) -> int: """Second decimal digit of a number, counting from left.""" return str(n)[1] </pre> (-:

yang.wang04 on June 22, 2016, 4:05 a.m.
The use case is just from the example provided by bryukh as shown below: You should try to use the key parameter for sorting. <h1>sort by last digit for numbers from 10 to 99 only</h1> sorted([11, 20, 54, 73], key=lambda x: str(x)[1]) == [20, 11, 73, 54] It should be the last digit. :)

veky on June 22, 2016, 4:44 a.m.
You see, you can't fool me. ;-D

remakio on Aug. 19, 2015, 12:30 p.m.
Very beautifull!

veky on Aug. 19, 2015, 5:24 p.m.
Thanks. Have you seen <a href="http://www.checkio.org/mission/absolute-sorting/publications/veky/python-3/smn-theorem/?ordering=most_voted">this one</a>? :-)

hallux on Dec. 26, 2015, 1:57 a.m.
I knew you could provide a key for sort(), but didn't know you could for sorted() as well.

veky on Dec. 26, 2015, 6:30 a.m.
They have the same interface. <pre class='brush: python'>def sorted(it, **kwhatever): l = list(it) l.sort(**kwhatever) return l </pre>

hugoboss on Aug. 13, 2018, 12:13 p.m.
OK, it coincides with the condition: there is not a reason to create a function with full definition to pass it as an argument in the check_it. Lambda as a variable instead of a function with lambda as an argument to pass in it. It's more readable at least...

veky on Aug. 13, 2018, 5:17 p.m.
lambda-defined function is pretty much the same kind of object as def-defined function, the only distinction is expression/statement one. If you really want to see a "function without function", try <a href="https://py.checkio.org/mission/absolute-sorting/publications/veky/python-3/smn-theorem/?ordering=most_voted&filtering=all">this</a>. ;-9

hugoboss on Aug. 16, 2018, 8:22 p.m.
Yes, I have already checked out this veky-way of problem-solving. One import operation ... But there is a defined function here: functools.partial method:) What I wanted to learn more were lambdas and I have it done, thanks.

veky on Aug. 20, 2018, 3:27 p.m.
There is no functools.partial method. There is functools.partialmethod, but it's something almost completely different. ;-) The most important thing to learn about lambdas is when they are not the best choice, i.e. when they should be replaced by a better tool. Functools.partial is one of these tools in <a href="https://docs.python.org/3/library/asyncio-eventloop.html#calls">many</a> cases.

alekseykonotop on Sept. 28, 2018, 3:40 p.m.
Very, very cool and clear!!!

bsquare on Sept. 18, 2019, 2:02 p.m.
Quick and easy, good.

lifeshow30s on July 8, 2020, 4:15 p.m.
gotcha! lambda is a good way to write pythonic

veky on July 8, 2020, 6:17 p.m.
Exactly the wrong lesson here. You'll notice that I didn't write `key=lambda x:abs(x)` above. The only reason for the outer lambda is CiO's naming conventions. But otherwise, lambda is almost always unnecessary.

BraveCobra22 on Feb. 12, 2023, 9:49 p.m.
I don't get it.

veky on Feb. 15, 2023, 9:16 a.m.
Something specifically, or just a general idea?

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