ℤ ≅ ℕ × bool clear solution for Nearest Value by veky - python coding challenges

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ℤ ≅ ℕ × bool solution in Clear category for Nearest Value by veky

def nearest_value(values: set, one: int) -> int:
    def distance(value): return abs(value - one), value > one
    return min(values, key=distance)

March 18, 2019

Comments:

Oleg_Novikov on Nov. 20, 2019, 12:38 p.m.
Very nice solution!

igharok on April 1, 2020, 2:12 p.m.
Great trick with boolean as second sorting factor, thanks!

PHANTOM0308 on April 6, 2020, 8:54 p.m.
How does this "value > one" exactly work here?

veky on April 6, 2020, 9:37 p.m.
It's a bool. Bools are ordered. False is before True. That means that when two values have the same absolute distance, min will pick the one where that bool is False.

PHANTOM0308 on April 6, 2020, 9:39 p.m.
Learn something new today, thanks man!

Booplesnoot on June 5, 2020, 5:51 p.m.
What does ℤ ≅ ℕ × bool mean?

veky on June 5, 2020, 6 p.m.
That means that the structure of whole numbers (integers) is isomorphic to the Cartesian product of the structures of natural numbers and booleans. And now, what do you really want to know? :-)

koladen on Sept. 29, 2020, 4:46 a.m.
Will work without value > one, return abs(value - one), value

veky on Sept. 30, 2020, 2:54 p.m.
`abs`olutely. :-)

xiaoyangli.cityu on Oct. 16, 2020, 10:15 a.m.
really readable & educational!!

_Chico__5d82cee4f5234e78a5c65e on May 15, 2021, 6:45 a.m.
:O

veky on May 15, 2021, 7:07 a.m.
Oh yes, I forgot to add, I'm a professional mathematician. Sorry for the pun. ;-D

_Chico__5d82cee4f5234e78a5c65e on May 15, 2021, 7:14 a.m.
xD

sleepgoose on May 25, 2021, 2:06 a.m.
wow,amazing!I learned a lot in the code and comments.

jake99 on July 12, 2021, 10:31 p.m.
just to make sure im understanding this correctly, the second line returns somthing similar to this right? so for nearest_value({4, 7, 10, 11, 12, 17}, 9) it would be... {(5,False), (2,False), (1,True), (2,True), (3,True), (5,True)}

veky on July 13, 2021, 4:45 a.m.
... except there is no set such as what you describe, only its values (one by one).

jake99 on July 13, 2021, 4:48 a.m.
ok thanks, i was having trouble debugging this so i had to ask. i think i have to look up exactly how the key argument works, i know what it does but not how it does it.

veky on July 13, 2021, 4:57 a.m.
You can think of it this way (not exactly how it works, but the differences are technical): first a list of all the elements of an argument is constructed. Then a parallel list of all the key values is made. Then the second list is sorted, its elements dragging the elements from the first list with them whenever they are swapped during the sort. Alternatively, you can imagine that for every element `x` of an argument, a pair `(key(x), x)` is constructed. Then a list of such pairs is sorted (by first coordinate), and from the sorted list of pairs only second coordinate are extracted. The process is know in Perl community as <a href="https://en.wikipedia.org/wiki/Schwartzian_transform">Schwartzian transform</a>. For debugging, you can simply print the argument and/or the return value inside the `distance` function at every call. You can use an already made decorator for that, available at <a href="https://stackoverflow.com/a/32238541/1875565">Stack Overflow</a>.

viktor.chyrkin on Aug. 15, 2021, 3:14 p.m.
really good but this is better: def nearest_value(values: set, one: int) -> int: return min(values, key=lambda value: (abs(value - one), value > one))

veky on Aug. 15, 2021, 7:39 p.m.
Well, in some ways it's better, in some other ways it's worse. For example, it is a line much longer than 72 characters. :-P Also, I'm already accused of overusing lambdas all the time here. :-)

nimay on Sept. 7, 2021, 9:45 a.m.
Your solution cool, but it don't work with values: assert nearest_value({0, -2}, 0) == -2

veky on Sept. 7, 2021, 10:33 a.m.
I don't understand. My solution doesn't give -2 but 0, and it is correct as far as I see.

Verstov on Oct. 1, 2021, 7:34 p.m.
cool!

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