Ruby convert array of hashes into one hash

Question

The input hash array is something like this:

[{count: 111, date: A},{count: 222, date: B},{count: 333, date: C}]

I want convert it into:

{A => {count: 111}, B => {count: 222}, C => {count: 333}}

That's just a simplified version, the hash could be very large - I mean many keys.

Answer 1

a = [{count: 111, date: 'A'},{count: 222, date: 'B'},{count: 333, date: 'C'}]
Hash[a.map {|h| [h[:date], {count: h[:count]}]}]
# => {"A"=>{:count=>111}, "B"=>{:count=>222}, "C"=>{:count=>333}}

Answer 2

aoh = [{count: 111, date: 'A'},{count: 222, date: 'B'},{count: 333, date: 'C'}]
flat = Hash[aoh.map {|h| [h.delete(:date), h]}]
# => {"A"=>{:count=>111}, "B"=>{:count=>222}, "C"=>{:count=>333}}

This is simliar to @falsetru's solution, but slightly more general in that if there are more keys in the original hashes besides just :count and :date , they will all be preserved in the result:

aoh = [{count: 111, date: 'A', pos: 1},{count: 222, date: 'B', pos: 2},{count: 333, date: 'C', pos: 3}]
flat = Hash[aoh.map {|h| [h.delete(:date), h]}]
# => {"A"=>{:count=>111, :pos=>1}, "B"=>{:count=>222, :pos=>2}, "C"=>{:count=>333, :pos=>3}}

Answer 3

The Array#inject method is a good choice:

[{count: 111, date: 'A'},{count: 222, date: 'B'},{count: 333, date: 'C'}].inject({}) do |h, item|
  h[item[:date]] = {count: item[:count]}
  h
end