Ruby - CSV from hash with values for each key stored vertically

Question

Need pointers on writing a hash to a csv with keys forming the column names and the key values being the column values.

Hash is of the format as below

hash = { 'A' => [ 'v', 'x', 'y' , 'z' ] , 'B' => [ 'm', 'n' , 'o' ] , 
'C' => [ 'i', 'j' , 'k' , 'l', 'm', 'n' , 'o' ] }

Desired CSV output

row 0 (headers) - 'A' , 'B' , 'C'
row 1           - 'v' , 'm' , 'i'
row 2           - 'x' , 'n' , 'j'
row 3           - 'y' , 'o' , 'k'
row 4           - 'z' , ''  , 'l'
row 5           - ''  , ''  , 'm'
row 6           - ''  , ''  , 'n'
row 7           - ''  , ''  , 'o'

Tried the following -

csv = CSV.open ("file.csv" , 'wb', headers: true)
hash.each do |k, v|
csv[k] = v         # CSV::Table has a []= method
end

Was thinking csv[k] = v should work, but it doesn't.

Victor Moroz · Accepted Answer · 2014-01-26 17:28:08Z

1

CSV.open("/tmp/file.csv", 'wb') do |csv|
   csv << hash.keys
   max_len = hash.values.map(&:length).max
   (0...max_len).zip(*hash.values).each do |_, *row|
    csv << row
  end
end

EDIT I initially used row.compact to match your output, but it doesn't seem to be consistent. Row 4 should look like "z,", not "z"

edited Jan 26, 2014 at 17:28

answered Jan 26, 2014 at 16:56

Victor Moroz

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2 Comments

user3206440 Over a year ago

I just edited the question. The approach works to some extend, but falls a tad short of matching the output. This seems iterate only up the number of values for the first key in the hash. So row 5, 6 and 7 above never gets written into the csv.

Victor Moroz Over a year ago

Right, I overlooked this scenario. Edited my answer.

Arup Rakshit · Accepted Answer · 2014-02-23 21:58:51Z

I would do the same as below :

require 'csv'

output_file_path = File.expand_path('output.csv',File.dirname(__FILE__))

hash = {   
           'A' => [ 'v', 'x', 'y' , 'z' ] ,
           'B' => [ 'm', 'n' , 'o' ] ,
           'C' => [ 'i', 'j' , 'k' , 'l', 'm', 'n' , 'o' ]
       }

option = { 
           :headers => hash.keys,
           :write_headers => true,
           :force_quotes => true,
           :converters => CSV::Converters[:nil_to_string] = lambda do |field| 
             field.to_s
           end
         }
max_value_size = hash.values.map(&:size).max

CSV.open(output_file_path,'w',option) do |csv|
  key_ary = hash.keys
  max_value_size.times do |index|
    csv << key_ary.map { |k| hash[k][index] } 
  end
end

output :

"A","B","C"
"v","m","i"
"x","n","j"
"y","o","k"
"z","","l"
"","","m"
"","","n"
"","","o"

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