[#74190] [Ruby trunk Feature#12134] Comparison between `true` and `false` — duerst@...
SXNzdWUgIzEyMTM0IGhhcyBiZWVuIHVwZGF0ZWQgYnkgTWFydGluIETDvHJzdC4KCgpUc3V5b3No
3 messages
2016/03/07
[#74269] Type systems for Ruby — Rob Blanco <ml@...>
Dear ruby-core,
5 messages
2016/03/10
[#74395] [Ruby trunk Feature#12142] Hash tables with open addressing — shyouhei@...
Issue #12142 has been updated by Shyouhei Urabe.
3 messages
2016/03/17
[ruby-core:74570] [Ruby trunk Feature#12217] Introducing Enumerable#sum for precision compensated summation and revert r54237
From:
akr@...
Date:
2016-03-25 13:21:22 UTC
List:
ruby-core #74570
Issue #12217 has been updated by Akira Tanaka.
File inject-plus.txt added
I think sum of elements of an enumerable is used in many situations.
I searched '\.inject[ \(\{]' and '+' in .rb files in gems:
inject-plus.txt
It seems .inject(:+) is an idiom for summation.
```
% fgrep '.inject(:+)' inject-plus.txt|wc -l
1040
% fgrep '.inject(&:+)' inject-plus.txt|wc -l
446
% fgrep '.inject(0, :+)' inject-plus.txt|wc -l
138
% fgrep '.inject(0, &:+)' inject-plus.txt|wc -l
90
% fgrep '.inject(0.0, :+)' inject-plus.txt|wc -l
13
% fgrep '.inject(0.0, &:+)' inject-plus.txt|wc -l
23
```
It seems .inject {|s,e| s + e} is also used.
```
% grep '.inject(0) *{|\([a-z0-9]\+\), *\([a-z0-9]\+\)| *\1 *+ *\2 *}' inject-plus.txt|wc -l
311
% grep '.inject *{|\([a-z0-9]\+\), *\([a-z0-9]\+\)| *\1 *+ *\2 *}' inject-plus.txt|wc -l
213
% grep '.inject(0.0) *{|\([a-z0-9]\+\), *\([a-z0-9]\+\)| *\1 *+ *\2 *}' inject-plus.txt|wc -l
27
```
I think Enumerable#sum is useful:
- Enumerable#sum is shorter than Enumerable#inject(:+) ant it makes code succinct.
- it can return 0 for empty enumerable. It makes us to avoid bugs on empty enumerable.
- more accurate for sum of Floats by Kahan's compensated summation algorithm (as muraken said)
- faster than Enumerable#inject(:+) (Enumerable#inject(:+) will also be faster since Ruby 2.4, though)
However it has a problem:
- Enumerable#sum is not well defined for non-numeric elements, especially objects without + method.
----------------------------------------
Feature #12217: Introducing Enumerable#sum for precision compensated summation and revert r54237
https://bugs.ruby-lang.org/issues/12217#change-57697
* Author: Kenta Murata
* Status: Assigned
* Priority: Normal
* Assignee: Yukihiro Matsumoto
----------------------------------------
In this issue I propose to introduce Enumerable#sum for precision compensated summation of an array of floating point numbers.
In r54237, I've changed Enumerable#inject to support precision compensated summation for summing up floating point numbers.
But I noticed that this commit broke the equality of `ary.inject(:+) == ary.inject {|a, x| a + x }`.
I think this equality is important property of inject method, so I don't want to break it.
And because precision compensated algorithms are complicated, I think they are provided in the standard library, especially simple summation.
---Files--------------------------------
inject-plus.txt (1.21 MB)
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