Ruby - Generate an array of hashes from two nested arrays

Question

I have two nested arrays which look like

a = [["Codereview", 72], ["Exercise", 380], ["Prework", 220], ["Retrospective", 36]]
b = [["Codereview", 72], ["Exercise", 335], ["Prework", 118], ["Retrospective", 36]]

You can assume that the length of the arrays is always the same.

I would like to generate an array of hashes from these two nested arrays which should look like

data = [
 { name: "Codereview", total_marks: 72, student_marks: 72 },
 { name: "Exercise", total_marks: 380, student_marks:  335 },
 { name: "Prework", total_marks: 220, student_marks: 118 },
 { name: "Retrospective", total_marks: 36, student_marks: 36 }
]

I don't have an idea how to go about this. Any help would be appreciated.

Philip Hallstrom · Accepted Answer · 2016-09-05 16:48:52Z

1

This assumes that the length of both arrays is the same and their order matches up (as far as names go).

> a.zip(b).map{|e| {name: e.first.first, total_marks: e.first.last, student_marks: e.last.last}}

=> [{:name=>"Codereview", :total_marks=>72, :student_marks=>72},
 {:name=>"Exercise", :total_marks=>380, :student_marks=>335},
 {:name=>"Prework", :total_marks=>220, :student_marks=>118},
 {:name=>"Retrospective", :total_marks=>36, :student_marks=>36}]

answered Sep 5, 2016 at 16:48

Philip Hallstrom

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1 Comment

Cary Swoveland Over a year ago

If they don't necessarily have the same order, a.zip(b.sort_by { |bname,_| a.index { |aname,_| aname==bname } }).map.....

tessie · Accepted Answer · 2016-09-05 16:54:53Z

0

simple way.copying from console

 pry(main)> data =[]
 => []
 3] pry(main)> b_hash =b.to_h
 => {"Codereview"=>72, "Exercise"=>335, "Prework"=>118,Retrospective"=>36}
 pry(main)> a.each do |array|
 [8] pry(main)*   h = Hash.new()
 [8] pry(main)*   h["name"] = array.first
 [8] pry(main)*   h["total_marks"] = array.last
 [8] pry(main)*   h["student_marks"] = b_hash[array.first]
 [8] pry(main)*   data << h
 [8] pry(main)* end
 9] pry(main)> data
 => [{"name"=>"Codereview", "total_marks"=>72, "student_marks"=>72},
 {"name"=>"Exercise", "total_marks"=>380, "student_marks"=>335},
 {"name"=>"Prework", "total_marks"=>220, "student_marks"=>118},
 {"name"=>"Retrospective", "total_marks"=>36, "student_marks"=>36}]

answered Sep 5, 2016 at 16:54

tessie

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Comments

Cary Swoveland · Accepted Answer · 2016-09-05 18:51:53Z

a = [["Codereview", 72], ["Exercise", 380], ["Prework", 220], ["Retrospective", 36]]
b = [["Prework", 118], ["Retrospective", 36], ["Codereview", 72], ["Exercise", 335]]

g = a.each_with_object({}) { |(str, val), h| h[str] = { "name"=>str, "total_marks"=>val } }
  #=> {"Codereview"=>{"name"=>"Codereview", "total_marks"=>72},
  #    "Exercise"=>{"name"=>"Exercise", "total_marks"=>380},
  #    "Prework"=>{"name"=>"Prework", "total_marks"=>220},
  #    "Retrospective"=>{"name"=>"Retrospective", "total_marks"=>36}} 
b.each_with_object(g) { |(str, val),h| h[str]["student_marks"] = val }.values
  #=> [{"name"=>"Codereview", "total_marks"=>72, "student_marks"=>72},
  #    {"name"=>"Exercise", "total_marks"=>380, "student_marks"=>335},
  #    {"name"=>"Prework", "total_marks"=>220, "student_marks"=>118},
  #    {"name"=>"Retrospective", "total_marks"=>36, "student_marks"=>36}]

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