Order/randomize/convert array in rails

Question

Hi,

I've got this:

a = [[123,1],[124,1],[125,1],[126,2],[127,3],[128,3]]

And I would like to turn a into b:

• ordered by value
• random within array of value

// updated:

b = [[124,123,125],[126],[128,127]]

How to do this in ruby? Im using rails.

Answer 1

One solution is:

a = [[123,1],[124,1],[125,1],[126,2],[127,3],[128,3]]

a = a.sort {|d, e| d[1] <=> e[1]}

prev = a[0][1]; result = []; group = [];

a.each do |e|
  if e[1] == prev
    group << e[0]
  else
    result << group.shuffle
    group = [e[0]]
    prev = e[1]
  end
end
result << group

p result

run:

$ ruby t.rb
[[125, 123, 124], [126], [127, 128]]

Answer 2

a.group_by(&:last).
  sort_by(&:first).
  map(&:last).
  map {|el| el.map(&:first).shuffle }

Answer 3

a.reduce([]){|m,i|m[i[1]]=(m[i[1]]||[])<<i[0];m}.compact