Ruby/Rails: Convert array of arrays to hash of arrays

Question

I'm looking for an idiomatic way of querying the database and have all the values grouped by column.

For example, the instruction:

@players = Player.pluck(:white, :black, :red, :blue, :yellow)

Returns a multi-dimensional array like this:

[[1, 2, 3, 4, 5], [6, 7, 8, 9, 10], [11, 12, 13, 14, 15]]

but I need a hash of arrays like this:

{
  white:  [1, 6, 11],
  black:  [2, 7, 12], 
  red:    [3, 8, 13],
  blue:   [4, 9, 14],
  yellow: [5, 10, 15]
}

Where the first element of all arrays is stored with the 'white' key, the second element of all arrays is stored with the 'black' key and so on.

falsetru · Accepted Answer · 2013-09-12 13:57:53Z

8

a = [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10], [11, 12, 13, 14, 15]]
[:white, :black, :red, :blue, :yellow].zip(a.transpose)
# => [[:white, [1, 6, 11]], [:black, [2, 7, 12]], [:red, [3, 8, 13]], [:blue, [4, 9, 14]], [:yellow, [5, 10, 15]]]
Hash[[:white, :black, :red, :blue, :yellow].zip(a.transpose)]
# => {:white=>[1, 6, 11], :black=>[2, 7, 12], :red=>[3, 8, 13], :blue=>[4, 9, 14], :yellow=>[5, 10, 15]}

answered Sep 12, 2013 at 13:57

falsetru

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