Convert hash keys to lowercase -- Ruby Beginner

Question

My table field names are lowercase and the field names I get from CSV files are camelcase. Is there anyway I can convert the keys of an array of hashes to lowercase?

Here is the code I have right now:

    CSV.foreach(file, :headers => true) do |row|
      Users.create!(row.to_hash)
    end

This is failing because the keys are camel case (I've verified this by manually editing the file to make the header row all lowercase).

PS. Also I would love to know why the hell rails takes table field names' case sensitivity into play to begin with?

score 26 · Answer 1 · answered Apr 03 '13 at 14:06

You can just use the header_converters option with CSV:

CSV.foreach(file, :headers => true, :header_converters => lambda { |h| h.try(:downcase) }) do |row|
  Users.create!(row.to_hash)
end

Important to put the .try in there since an empty header will throw an exception. Much better (and faster) than doing this on every row.

score 16 · Accepted Answer · answered Nov 02 '11 at 12:29

16

You can use something like this:

CSV.foreach(file, :headers => true) do |row|
  new_hash = {}
  row.to_hash.each_pair do |k,v|
   new_hash.merge!({k.downcase => v}) 
  end

  Users.create!(new_hash)
end

I had no time to test it but, you can take idea of it.
Hope it will help

answered Nov 02 '11 at 12:29

bor1s

4,081
18
25

That works! But I'm also curious as to why the heck rails would enforce case here (my file system isn't case sensitive so that is not the issue). – Hopstream Nov 02 '11 at 12:36
Excuse me, but I do not unserstand what do you mean saying: rails takes table field names' case sensitivity into play to begin with? :) (Maybe this is my bad english knowledge :) ) – bor1s Nov 02 '11 at 13:47
Meaning why does rails require case of field names in table to match the keys in the hash during insertion – Hopstream Nov 02 '11 at 13:52
3

Why wouldn't it? Your DB is (probably) case-sensitive, and Rails just passes the names through. – Marnen Laibow-Koser Nov 02 '11 at 13:57

score 10 · Answer 3 · answered Jan 08 '19 at 10:48

You can simple do

hash.transform_keys(&:downcase)

to change hash keys to lowercase, or you can also transform hash values to lowercase or upper case as per your requirement.

hash.transform_values(&:downcase) or hash.transform_values(&:upcase)

hash = {:A=>"b", :C=>"d", :E=>"f"}
hash.transform_keys(&:downcase)
=> {:a=>"b", :c=>"d", :e=>"f"}

score 6 · Answer 4 · answered Mar 13 '17 at 15:33

6

Since this was tagged with Rails.

With ActiveSupport starting vom version 3.0 you can use a HashWithIndifferentAccess.

That will allow lower/uppercase/symbol writing to access the keys or your Hash.

my_hash = { "camelCase": "some value" }
my_hash.with_indifferent_access[:camelcase] # 'some value'
my_hash.with_indifferent_access['camelcase'] # 'some value'
my_hash.with_indifferent_access['camelCase'] # 'some value'
my_hash.with_indifferent_access['CAMELCASE'] # 'some value'

ActiveSupport 4.0.2 also introduced this:

my_hash.deep_transform_keys!(&:downcase)
# or if your hash isn't nested:
my_hash.transform_keys!(&:downcase)

answered Mar 13 '17 at 15:33

neongrau

933
9
12

6

`with_indifferent_access` is supporting string-or-symbol, but is *not case insensitive* for me. ActiveSupport 5.0.4. – Justin Maxwell Jul 21 '17 at 12:06
Same as Justin Maxwell here. I used an alternative instead. – el n00b Apr 05 '18 at 14:47

score 4 · Answer 5 · answered Jul 23 '12 at 23:34

Ruby 1.9 provides quite a nice way to achieve this, using each_with_object to avoiding initialising a temporary variable.

CSV.foreach(file, :headers => true) do |row|
  new_hash = row.each_with_object({}) do |(k, v), h|
    h[k.downcase] = v
  end

  Users.create!(new_hash)
end

score 3 · Answer 6 · answered Oct 18 '16 at 14:27

3

I find this approach more elegant:

hash_with_camelcase_keys.to_a.map { |pair| [pair.first.downcase, pair.last] }.to_h

answered Oct 18 '16 at 14:27

Vlatka

33
1
2

1

`to_a.map { |key, value| [key.upcase.to_s, value] }.to_h` looks cleaner to me. – Sig May 18 '20 at 08:16

score 1 · Answer 7 · answered Jul 10 '12 at 02:06

I would add the hash directly, more efficient than merge! because you're not creating a new hash for every pair.

CSV.foreach(file, :headers => true) do |row|
  new_hash = {}
  row.to_hash.each_pair do |k,v|
   new_hash[k.downcase] = v 
  end

  Users.create!(new_hash)
end

score 1 · Answer 8 · answered Jul 28 '13 at 19:56

1

I found that this solution is significantly faster and a bit more "Rubyish".

CSV.foreach(file, :headers => true) do |row|
  new_hash = Hash[row.to_hash.map { |k, v| [k.downcase, v] }]
  Users.create!(new_hash)
end

answered Jul 28 '13 at 19:56

Not sure it is more rubyish - it uses a class or module method which even uses a method ending in ! – shevy Jun 12 '14 at 20:25

score 1 · Answer 9 · answered Jun 25 '20 at 13:12

You could consider using underscore instead of downcase because this would also transform the CamelCase to camel_case notation, which is more Rubylike.

My personal preferences goes to using deep_transform_keys: hash.deep_transform_keys{|key| key.underscore.to_sym }

As transform_keys do not traverse the whole hash.

Convert hash keys to lowercase -- Ruby Beginner

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