将哈希值按一个键值分组，同时将其他键值合并到一个字符串中

Question

I've seen a lot of similar questions around, but this is a very specific case.

What I have as input:

entries = [
   {:action=>"X", :sequence=>1},
   {:action=>"Y", :sequence=>2},
   {:action=>"W", :sequence=>2},
   {:action=>"Z", :sequence=>3}
]

What I want as output (join actions by sequence with "and" and all actions with ", "):

"X, Y and W, Z"

How I've done it:

group = entries.group_by {|x| x.delete(:sequence)}.values
=> [[{:action=>"X"}], [{:action=>"Y"}, {:action=>"W"}], [{:action=>"Z"}]]

array = group.map { |el| el.map { |h| h[:action] } }
=> [["X"], ["Y", "W"], ["Z"]]

string = array.map { |a| a.join(' and ') }.join(', ')
=> "X, Y and W, Z"

It works, but its far from being clean. Does anyone have a better solution?

Answer 1

The below is the shortest one I can think of:

entries.group_by { |e| e.delete :sequence }
       .values
       .map { |e| e.map(&:values).join ' and ' }
       .join ', '

Another one [non-destructive]:

entries.map(&:values)
       .group_by(&:last)
       .values
       .map { |e| e.map(&:first).join ' and ' }
       .join ', '

And even:

 entries.map(&:values)
        .group_by(&:pop)
        .values
        .map { |e| e.join ' and ' }
        .join ', '

Answer 2

Or you may play with each_with_object method:

entries.each_with_object(Hash.new {[]}) do |e, m|
  m[e[:sequence]] <<= e[:action]
end.values
   .map{|e| e.join(' and ')}
   .join(", ")
#=> "X, Y and W, Z"