[#65451] [ruby-trunk - Feature #10333] [PATCH 3/1] optimize: "yoda literal" == string — ko1@...
Issue #10333 has been updated by Koichi Sasada.
9 messages
2014/10/07
[#65458] Re: [ruby-trunk - Feature #10333] [PATCH 3/1] optimize: "yoda literal" == string
— Eric Wong <normalperson@...>
2014/10/07
ko1@atdot.net wrote:
[#65502] Re: [ruby-trunk - Feature #10333] [PATCH 3/1] optimize: "yoda literal" == string
— Eric Wong <normalperson@...>
2014/10/08
Eric Wong <normalperson@yhbt.net> wrote:
[#65538] Re: [ruby-trunk - Feature #10333] [PATCH 3/1] optimize: "yoda literal" == string
— Eric Wong <normalperson@...>
2014/10/09
Eric Wong <normalperson@yhbt.net> wrote:
[#65549] Re: [ruby-trunk - Feature #10333] [PATCH 3/1] optimize: "yoda literal" == string
— SASADA Koichi <ko1@...>
2014/10/09
On 2014/10/09 11:04, Eric Wong wrote:
[#65551] Re: [ruby-trunk - Feature #10333] [PATCH 3/1] optimize: "yoda literal" == string
— Eric Wong <normalperson@...>
2014/10/09
SASADA Koichi <ko1@atdot.net> wrote:
[#65453] [ruby-trunk - Feature #10328] [PATCH] make OPT_SUPPORT_JOKE a proper VM option — ko1@...
Issue #10328 has been updated by Koichi Sasada.
3 messages
2014/10/07
[#65559] is there a name for this? — Xavier Noria <fxn@...>
When describing stuff about constants (working in their guide), you often
7 messages
2014/10/09
[#65560] Re: is there a name for this?
— Nobuyoshi Nakada <nobu@...>
2014/10/09
On 2014/10/09 20:41, Xavier Noria wrote:
[#65561] Re: is there a name for this?
— Xavier Noria <fxn@...>
2014/10/09
On Thu, Oct 9, 2014 at 1:59 PM, Nobuyoshi Nakada <nobu@ruby-lang.org> wrote:
[#65566] [ruby-trunk - Feature #10351] [Open] [PATCH] prevent CVE-2014-6277 — shyouhei@...
Issue #10351 has been reported by Shyouhei Urabe.
3 messages
2014/10/09
[#65741] Re: [ruby-cvs:55121] normal:r47971 (trunk): test/ruby/test_rubyoptions.rb: fix race — Nobuyoshi Nakada <nobu@...>
On 2014/10/16 10:10, normal@ruby-lang.org wrote:
5 messages
2014/10/16
[#65742] Re: [ruby-cvs:55121] normal:r47971 (trunk): test/ruby/test_rubyoptions.rb: fix race
— Eric Wong <normalperson@...>
2014/10/16
Nobuyoshi Nakada <nobu@ruby-lang.org> wrote:
[#65750] Re: [ruby-cvs:55121] normal:r47971 (trunk): test/ruby/test_rubyoptions.rb: fix race
— Tanaka Akira <akr@...>
2014/10/16
2014-10-16 12:48 GMT+09:00 Eric Wong <normalperson@yhbt.net>:
[#65753] [ruby-trunk - Feature #10333] [PATCH 3/1] optimize: "yoda literal" == string — ko1@...
Issue #10333 has been updated by Koichi Sasada.
3 messages
2014/10/16
[#65818] [ruby-trunk - Feature #10351] [PATCH] prevent CVE-2014-6277 — shyouhei@...
Issue #10351 has been updated by Shyouhei Urabe.
3 messages
2014/10/20
[ruby-core:65452] [ruby-trunk - Feature #8887] min(n), max(n), min_by(n), max_by(n)
From:
davidegrayson@...
Date:
2014-10-07 03:20:04 UTC
List:
ruby-core #65452
Issue #8887 has been updated by David Grayson.
Hello. I think the Ruby team should reconsider the ordering of the array returned by `max` and `max_by` when the `n` argument is provided. It makes much more sense to me that it would be sorted in descending order, meaning that the most extreme/special element would be first. For example, I would expect `max` to behave like this:
[1, 2, 10, 22, 23].max(3) # => [23, 22, 10]
It seems that min/min_by and max/max_by should be mirrors of each other. For example, I would expect that `max_by(n) { |x| x.foo }` would be equivalent to `min_by(n) { |x| -x.foo }`, assuming that `foo` returns a number.
That leaves us with two choices for the sorting: put the most extreme element first, or put the most extreme element last. I think putting the most extreme element first makes the most sense. Whenever I see any list of top-ranked items, the highest-ranked item is usually first. Here are some examples from the internet: http://imgur.com/a/MPsJl
I looked around on StackOverflow.com for Ruby users who might benefit from the new argument to min/min_by/max/max_by. Almost everyone asking a question about it wanted to use something like `max_by` and wanted to have the most extreme element be listed first:
* http://stackoverflow.com/questions/19804696
* http://stackoverflow.com/questions/11094874
* http://stackoverflow.com/questions/9390444
However, I should note that in one case, the questioner wanted the order of the original enumerable to be preserved (http://stackoverflow.com/questions/9459447), and in another case they didn't specify (http://stackoverflow.com/questions/12241165). I didn't find anyone who wanted the most extreme element to be last.
I also looked for similar features in other programming languages. The closest thing I found was Python's `heapq.nlargest` method, which does return the most extreme element first:
https://docs.python.org/3/library/heapq.html#heapq.nlargest
In SQL, if you are making a query to get the top 10 rows, I think you must do something like this, which puts the most extreme row first:
select * from players order by score desc limit 10
In conclusion, I think it is more natural for the `max` and `max_by` methods to return arrays with the most extreme element first. I hope the Ruby team will do this before Ruby 2.2.0 is released, since it will be hard to change it later without breaking a lot of people's code.
--David Grayson
P.S. Some other Ruby developers I know here in Las Vegas have agreed with this letter and wanted their names to be included:
* Jason Arhart
* Paul Grayson
----------------------------------------
Feature #8887: min(n), max(n), min_by(n), max_by(n)
https://bugs.ruby-lang.org/issues/8887#change-49236
* Author: Akira Tanaka
* Status: Closed
* Priority: Normal
* Assignee: Akira Tanaka
* Category: core
* Target version:
----------------------------------------
How about adding an optional argument, n, for Enumerable#{min,max,min_by,max_by} to
return minimum/maximum n elements as an array.
Example:
* [6, 0, 3, 3, 8, 3, 5, 0, 6].min(4) #=> [0, 0, 3, 3]
* [6, 0, 3, 3, 8, 3, 5, 0, 6].max(4) #=> [5, 6, 6, 8]
* [6, 0, 3, 3, 8, 3, 5, 0, 6].min_by(4) {|v| (v-5)**2 } #=> [5, 6, 6, 3]
* [6, 0, 3, 3, 8, 3, 5, 0, 6].max_by(4) {|v| (v-5)**2 } #=> [3, 8, 0, 0]
These methods are similar to sort follows first or last.
* e.min(n) is similar to e.sort.first(n)
* e.max(n) is similar to e.sort.last(n)
* e.min_by(n) {...} is similar to e.sort_by {...}.first(n)
* e.max_by(n) {...} is similar to e.sort_by {...}.last(n)
However e.min(n), e.max(n), e.min_by(n), e.max_by(n) are
less memory consuming and can be faster.
They use memory proportional to n, not e.
They doesn't sort whole e.
I feel their use is not rare.
I found several use after searching.
[ruby-talk:123508], [ruby-list:40939], [ruby-talk:273980]
http://d.hatena.ne.jp/mjh/20101024/1287901875
http://stackoverflow.com/questions/11094874/get-top-n-elements-from-ruby-array-of-hash-values
http://www.math.kobe-u.ac.jp/~kodama/tips-ruby-sized_pqueue.html
https://bitbucket.org/sterlingcamden/topn
Also, e.max(n) can be used to implement weighted random sampling.
Pavlos S. Efraimidis, Paul G. Spirakis
Weighted random sampling with a reservoir
Information Processing Letters
Volume 97, Issue 5 (16 March 2006)
```
% ./ruby -e '
module Enumerable
def wsample(n)
self.max_by(n) {|v| rand ** (1.0/yield(v)) }
end
end
e = (-20..20).to_a*10000
a = e.wsample(20000) {|x|
Math.exp(-(x/5.0)**2) # normal distribution
}
# a is 20000 samples from e.
p a.length
h = a.group_by {|x| x }
-10.upto(10) {|x| puts "*" * (h[x].length/30.0).to_i if h[x] }
'
20000
*
***
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***
*
```
Any comments?
---Files--------------------------------
min-n-and-max-n.patch (15.2 KB)
maxn.pdf (20.3 KB)
--
https://bugs.ruby-lang.org/