Question

I have an array of arrays like so:

[[1,"A"], [1,"B"], [2,"C"], [2,"D"]]

I’d like to get the results into a Hash like so:

1 => {results => ["A","B"]}, 2 => {results => ["C","D"]}

I tried using the “group_by” methods and wasn’t able to get it into this form. What’s the most efficient way to do this?

Any ideas?

Answer 1

Is this what you want?

irb(main):001:0> a=[[1,"A"], [1,"B"], [2,"C"], [2,"D"]]
=> [[1, "A"], [1, "B"], [2, "C"], [2, "D"]]

irb(main):002:0> h={}
=> {}

irb(main):003:0> a.each { |k,v| h[k] ||= []; h[k] << v }
=> [[1, "A"], [1, "B"], [2, "C"], [2, "D"]]

irb(main):004:0> h
=> {1=>["A", "B"], 2=>["C", "D"]}

Or, if you really want a hashtable of hashtable with a ‘result’ key:

irb(main):003:0> a.each { |k,v| h[k] ||= {}; h[k]['result'] ||= []; h[k]['result'] << v }
=> [[1, "A"], [1, "B"], [2, "C"], [2, "D"]]
irb(main):004:0> h
=> {1=>{"result"=>["A", "B"]}, 2=>{"result"=>["C", "D"]}}