Feature #18181
Updated by kyanagi (Kouhei Yanagita) over 2 years ago
PR is https://github.com/ruby/ruby/pull/4874
I propose `Enumerable#min_with_value`, `max_with_value` and `minmax_with_value`.
These methods work like this:
``` ruby
%w(abcde fg hijk).min_with_value { |e| e.size } # => ['fg', 2]
%w(abcde fg hijk).max_with_value { |e| e.size } # => ['abcde', 5]
%w(abcde fg hijk).minmax_with_value { |e| e.size } # => [['fg', 2], ['abcde', 5]]
```
## Motivation Motivation:
When I use `Enumerable#min_by`, I sometimes want to get not only the minimum element
but also the value from the given block.
(e.g.: There are many points. Find the nearest point and get distance to it.)
``` ruby
elem = enum.min_by { |e| foo(e) }
value = foo(elem)
```
This works, but I'd like to avoid writing foo() twice. (Consider a more complex case.)
This can be written without repeated foo() like belows, but it is slightly complicated and needs extra arrays.
``` ruby
value, elem = enum.map { |e| [foo(e), e] }.min_by(&:first)
```
If the size of enum is enormous, it is hard to use intermediate arrays.
`Enumerable#min_with_value` solves this problem.
I think `min_with_value` is the best name I could think of, but any suggestions for better names would be appreciated.
## Benchmark
https://bugs.ruby-lang.org/issues/18181#note-2
## Example
Solving a traveling salesman problem in nearest neighbor algorithm.
``` ruby
require 'set'
Point = Struct.new(:x, :y)
points = Set.new([Point.new(1, 1), Point.new(2, 4), Point.new(3, 3), Point.new(2, 2), Point.new(0, 1)])
total = 0
current = points.first
points.delete(current)
path = [current]
until points.empty?
current, distance = points.min_with_value do |point|
Math.hypot(current.x - point.x, current.y - point.y)
end
total += distance
points.delete(current)
path << current
end
p path
p total
```