Convert CSV file into array of hashes

Question

I have a csv file, some hockey stats, for example:

09.09.2008,1,HC Vitkovice Steel,BK Mlada Boleslav,1:0 (PP)
09.09.2008,1,HC Lasselsberger Plzen,RI OKNA ZLIN,6:2
09.09.2008,1,HC Litvinov,HC Sparta Praha,3:5

I want to save them in an array of hashes. I don't have any headers and I would like to add keys to each value like "time" => "09.09.2008" and so on. Each line should by accessible like arr[i], each value by for example arr[i]["time"]. I prefer CSV class rather than FasterCSV or split. Can you show the way or redirect to some thread where a similar problem was solved?

What is so on? Other than "time", we have no clue what keys you want. Maybe you should show the expected output. — sawa
– sawa, Commented Jan 7, 2013 at 16:25
so on.. I meant etc. , my english isn't probably so good. Other key could be round, home and visiting team and score. Expected Output is {["time" => "09.09.2008", "round" => "1", "home" => "Vitkovice Steel", "visiting" => "BK Mlada Boleslav", "score" => "1:0 (PP)"],[next lines...]} — Mythago
– Mythago, Commented Jan 7, 2013 at 16:45

Nathan Long · Accepted Answer · 2015-02-18 11:58:16Z

95

Just pass `headers: true`

CSV.foreach(data_file, headers: true) do |row|
  puts row.inspect # hash
end

From there, you can manipulate the hash however you like.

(Tested with Ruby 2.0, but I think this has worked for quite a while.)

Edit

You say you don't have any headers - could you add a header line to the beginning of the file contents after reading them?

edited Feb 18, 2015 at 11:58

answered Mar 28, 2014 at 19:36

Nathan Long

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2 Comments

Jared Beck Over a year ago

Technically, I think each row is an instance of CSV::Row, which acts like a Hash but doesn't actually inherit Hash.

Mr. Tim Over a year ago

You can also use CSV.parse(data, headers: true).map(&:to_h) to similar effect, taking into account Jared's note above. This turns your CSV into an array of hashes with headers as keys. You can also want to toss in the option header_converters: :symbol to use symbols as keys instead of the column name as strings.

AlexeyMK · Accepted Answer · 2017-09-13 22:09:37Z

45

This is a fantastic post by Josh Nichols which explains how to do what you're asking.

To summarize, here his code:

csv = CSV.new(body, :headers => true, :header_converters => :symbol, :converters => [:all, :blank_to_nil])
csv.to_a.map {|row| row.to_hash }
=> [{:year=>1997, :make=>"Ford", :model=>"E350", :description=>"ac, abs, moon", :price=>3000.0}, {:year=>1999, :make=>"Chevy", :model=>"Venture \"Extended Edition\"", :description=>nil, :price=>4900.0}, {:year=>1999, :make=>"Chevy", :model=>"Venture \"Extended Edition, Very Large\"", :description=>nil, :price=>5000.0}, {:year=>1996, :make=>"Jeep", :model=>"Grand Cherokee", :description=>"MUST SELL!\nair, moon roof, loaded", :price=>4799.0}]

So, you could save the body of your CSV file into a string called body.

body = "09.09.2008,1,HC Vitkovice Steel,BK Mlada Boleslav,1:0 (PP)
09.09.2008,1,HC Lasselsberger Plzen,RI OKNA ZLIN,6:2
09.09.2008,1,HC Litvinov,HC Sparta Praha,3:5"

And then run his code as listed above on it.

edited Sep 13, 2017 at 22:09

AlexeyMK

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answered Dec 30, 2013 at 19:23

CodeBiker

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5 Comments

shakerlxxv Over a year ago

Thanks for the post reference, very useful. I'm not sure if it was my data specifically; however, I needed to ommit the :blank_to_nil otherwise I was getting an error *** NoMethodError Exception: undefined method arity' for nil:NilClass`

user2012677 Over a year ago

@CodeBiker @shakerlxxv I have the same error message, NoMethodError: undefined method encode for nil:Nilclass. What is the solution to get it working?

shakerlxxv Over a year ago

@user2012677, I omitted the :blank_to_nil converter, so my final expression looks like

CSV.new(File.new(file), :headers => true, :header_converters => :symbol, :converters => [:all]).to_a.map {|row| row.to_hash }

tjmcewan Over a year ago

You can also reduce it to this: CSV.new(body, headers: true).map(&:to_hash) (in Ruby 2.1.5, at least)

kirhgoff Over a year ago

I like Pavel's solution above better

AJcodez · Accepted Answer · 2013-01-07 16:26:34Z

43

You can use the Ruby CSV parser to parse it, and then use Hash[ keys.zip(values) ] to make it a hash.

Example:

test = '''
09.09.2008,1,HC Vitkovice Steel,BK Mlada Boleslav,1:0 (PP)
09.09.2008,1,HC Lasselsberger Plzen,RI OKNA ZLIN,6:2
09.09.2008,1,HC Litvinov,HC Sparta Praha,3:5
'''.strip

keys = ['time', etc... ]
CSV.parse(test).map {|a| Hash[ keys.zip(a) ] }

answered Jan 7, 2013 at 16:26

AJcodez

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5 Comments

Mythago Over a year ago

I tried that 'require 'csv' csv_data = CSV.read 'data.txt' keys = ['time',"round","home","visiting","score"] CSV.parse(csv_data).map {|a| Hash[ keys.zip(a) ] }' but i probably didn catch the idea because it returned some errors

Mythago Over a year ago

c:/Ruby193/lib/ruby/1.9.1/csv.rb:1381:in ensure in parse': undefined method close' for #<Array:0x8f2050> (NoMethodError) from c:/Ruby193/lib/ruby/1.9.1/csv.rb:1381:in parse' from C:/Users/Mythago/My Documents/Aptana Studio 3 Workspace/elh stats/main.rb:5:in <main>'

AJcodez Over a year ago

looks like you're calling close on the array. Dont do that

David Unric Over a year ago

@user1955522 CSV.parse method accepts string as its argument, not an array. Try CSV.read('data.txt').map {|a| Hash[ keys.zip(a) ]} .

xhocquet Over a year ago

Beautiful code. This is a great example of Ruby's strengths!

Pavel Evstigneev · Accepted Answer · 2018-02-26 10:08:37Z

39

A little shorter solution

Parse string:

CSV.parse(content, headers: :first_row).map(&:to_h)

Parse file:

CSV.open(filename, headers: :first_row).map(&:to_h)

answered Feb 26, 2018 at 10:08

Pavel Evstigneev

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1 Comment

Damion Gomez Over a year ago

Parse file code lead to: /usr/lib/ruby/2.5.0/csv.rb:1764:in to_h': wrong element type String at 0 (expected array) (TypeError)`

lacostenycoder · Accepted Answer · 2022-07-20 14:36:00Z

8

Slight variation on Nathan Long's answer

data_file = './sheet.csv'
data = CSV.foreach(data_file, headers: true).map(&:to_h)

Now data is an array of hashes to do your bidding with!

edited Jul 20, 2022 at 14:36

answered Nov 18, 2016 at 15:48

lacostenycoder

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2 Comments

dekeguard Over a year ago

Even leaner: data = CSV.foreach(data_file, headers: true).map{ |row| row.to_h }

agbodike Over a year ago

Even leaner than that: data = CSV.foreach(data_file, headers: true).map(&:to_h) :D

Will Madden · Accepted Answer · 2018-04-24 15:39:04Z

2

The headers option to the CSV module accepts an array of strings to be used as the headers, when they're not present as the first row in the CSV content.

CSV.parse(content, headers: %w(time number team_1 team_2 score))

This will generate an enumerable of hashes using the given headers as keys.

answered Apr 24, 2018 at 15:39

Will Madden

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Comments

gaurav.singharoy · Accepted Answer · 2015-05-25 23:40:33Z

1

You can try the following gem also

require 'csv_hasher'
arr_of_hashes = CSVHasher.hashify('/path/to/csv/file')

The keys of the returned hashes will be the header values of the csv file.

If you want to pass your own keys then

keys = [:key1, :key2, ... ]
arr_of_hashers = CSVHasher.hashify('/path/to/csv/file', { keys: keys })

edited May 25, 2015 at 23:40

answered May 25, 2015 at 22:45

gaurav.singharoy

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Comments

SofiSun · Accepted Answer · 2022-03-21 13:38:15Z

1

I guess this is the shortest version:

keys = ["time", ...]
CSV.parse(content, headers: keys).map(&:to_h)

answered Mar 21, 2022 at 13:38

SofiSun

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Comments

Tilo · Accepted Answer · 2022-05-23 21:35:15Z

0

you could also use the SmarterCSV gem, which returns data from CSV files as Ruby hashes by default.

It has a lot of features, including processing the data in chunks, which is very benefitial for huge data files.

  require 'smarter_csv'

  options = {} # see GitHub README
  data = SmarterCSV.process(your_file_name, options)

answered May 23, 2022 at 21:35

Tilo

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Comments

Touseef Murtaza · Accepted Answer · 2023-12-28 07:51:40Z

0

For me

data_file = 'file.csv'
data = CSV.foreach(data_file, headers: true).map(&:to_h)

works as mentioned by lacostenycoder with that your csv file with the content let's say

id,amount
1,10.10
2,20.20

will be converted to

[{"id"=>"1", "amount"=>"10.10"},
 {"id"=>"2", "amount"=>"20.20"}]

answered Dec 28, 2023 at 7:51

Touseef Murtaza

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Just pass `headers: true`