ruby - 对数组数组进行分组并在 Ruby 中选择一些列

Question

我有这个数组:

    [[F1,State1,Blah1],[F2,State1,Blah2],[F1,State2,Blah3]]

什么是将上面的内容转换为的简洁 ruby​​ 方法:

    {State1=>[F1,F2],State2=>[F1]}

Answer 1

arr = [['F1','State1','Blah1'],['F2','State1','Blah2'],['F1','State2','Blah3']]

arr.group_by{|a| a[1]}.map {|k,v| [k, v.map(&:first)] }.to_h
# => {"State1"=>["F1", "F2"], "State2"=>["F1"]}