Best way to convert strings to symbols in hash

Question

What s the  fastest cleanest straightforward  way to convert all keys in a hash from strings to symbols in Ruby   This would be handy when parsing YAML   my hash   YAML load file  yml     I d like to be able to use   my hash  key     Rather than   my hash  key

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In ruby I find this to be the most simple and easy to understand way to turn string keys in hashes to symbols :

my_hash.keys.each { |key| my_hash[key.to_sym] = my_hash.delete(key)}

For each key in the hash we call delete on it which removes it from the hash (also delete returns the value associated with the key that was deleted) and we immediately set this equal to the symbolized key.

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In Ruby    2 5  docs  you can use   my hash transform keys  amp  to sym    Using older Ruby version  Here is a one-liner that will copy the hash into a new one with the keys symbolized   my hash   my hash inject      memo  k v   memo k to sym    v  memo    With Rails you can use   my hash symbolize keys my hash deep symbolize keys

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if you re using Rails  it is much simpler - you can use a HashWithIndifferentAccess and access the keys both as String and as Symbols   my hash with indifferent access    see also   http   api rubyonrails org classes ActiveSupport HashWithIndifferentAccess html    Or you can use the awesome  Facets of Ruby  Gem  which contains a lot of extensions to Ruby Core and Standard Library classes     require  facets     gt    some    gt   thing    foo    gt   bar   symbolize keys       gt     some  gt  thing    foo  gt  bar    see also  http   rubyworks github io rubyfaux  doc http   rubyworks github io facets docs facets-2 9 3 core json api-class-Hash

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Since Ruby 2 5 0 you can use Hash transform keys or Hash transform keys      a    gt  1   b    gt  2  transform keys  amp  to sym     gt    a   gt  1   b   gt  2

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The array we want to change  strings     quot HTML quot    quot CSS quot    quot JavaScript quot    quot Python quot    quot Ruby quot   Make a new variable as an empty array so we can  quot  push quot  the symbols in  symbols       Here s where we define a method with a block  strings each   x  symbols push x intern   End of code  So this is probably the most straightforward way to convert strings to symbols in your array s  in Ruby  Make an array of strings then make a new variable and set the variable to an empty array  Then select each element in the first array you created with the  quot  each quot  method  Then use a block code to  quot  push quot  all of the elements in your new array and use  quot  intern or  to sym quot  to convert all the elements to symbols  Symbols are faster because they save more memory within your code and you can only use them once  Symbols are most commonly used for keys in hash which is great  I m the not the best ruby programmer but this form of code helped me a lot If anyone knows a better way please share and you can use this method for hash too

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http   api rubyonrails org classes Hash html method-i-symbolize keys  hash      name    gt   Rob    age    gt   28    hash symbolize keys     gt    name   Rob   age   28

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Would something like the following work   new hash   Hash new my hash each    k  v  new hash k to sym    v     It ll copy the hash  but you won t care about that most of the time   There s probably a way to do it without copying all the data

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a shorter one-liner fwiw    my hash inject      h  k v   h merge   k to sym   gt  v

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For the specific case of YAML in Ruby  if the keys begin with      they will be automatically interned as symbols    require  yaml  require  pp  yaml str     connections    - host  host1 example com     port  10000   - host  host2 example com     port  20000   yaml sym      connections    -  host  host1 example com      port  10000   -  host  host2 example com      port  20000   pp yaml str   YAML load yaml str  puts yaml str keys first class pp yaml sym   YAML load yaml sym  puts yaml sym keys first class   Output        opt ruby-1 8 6-p287 bin ruby   test rb   connections         port   10000   host    host1 example com         port   20000   host    host2 example com     String   connections        port  10000   host   host1 example com         port  20000   host   host2 example com     Symbol

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So many answers here  but the one method rails function is hash symbolize keys

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In case the reason you need to do this is because your data originally came from JSON  you could skip any of this parsing by just passing in the  symbolize names option upon ingesting JSON   No Rails required and works with Ruby  1 9  JSON parse my json   symbolize names   gt  true

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This is not exactly a one-liner  but it turns all string keys into symbols  also the nested ones   def recursive symbolize keys my hash    case my hash   when Hash     Hash        my hash map do  key  value            key respond to   to sym    key to sym   key  recursive symbolize keys value          end         when Enumerable     my hash map    value  recursive symbolize keys value      else     my hash   end end

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ruby-1 9 2-p180  001  gt  h     aaa    gt  1   bbb    gt  2     gt    aaa   gt 1   bbb   gt 2   ruby-1 9 2-p180  002  gt  Hash h map  a   a first to sym  a last       gt    aaa  gt 1   bbb  gt 2

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Facets  Hash deep rekey is also a good option  especially    if you find use for other sugar from facets in your project  if you prefer code readability over cryptical one-liners    Sample   require  facets hash deep rekey  my hash   YAML load file  yml   deep rekey

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Starting on Psych 3 0 you can add the symbolize names  option  Psych load  --- n foo  bar        gt    foo   gt  bar    Psych load  --- n foo  bar   symbolize names  true        gt    foo  gt  bar    Note  if you have a lower Psych version than 3 0 symbolize names  will be silently ignored   My Ubuntu 18 04 includes it out of the box with ruby 2 5 1p57

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If you would like vanilla ruby solution and as me do not have access to ActiveSupport here is deep symbolize solution  very similar to previous ones       def deep convert element        return element collect    e  deep convert e    if element is a  Array        return element inject        sh  k v   sh k to sym    deep convert v   sh   if element is a  Hash        element     end

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I like this one-liner  when I m not using Rails  because then I don t have to make a second hash and hold two sets of data while I m processing it   my hash      a    gt  1   b    gt   string    c    gt  true    my hash keys each    key  my hash key to sym    my hash delete key     my hash   gt    a  gt 1   b  gt  string    c  gt true    Hash delete returns the value of the deleted key

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Even more terse   Hash my hash map   k v    k to sym v

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A modification to  igorsales answer  class Object   def deep symbolize keys     return self inject      memo  k v   memo k to sym    v deep symbolize keys  memo  if self is a  Hash     return self inject      memo v      memo            lt  lt  v deep symbolize keys  memo  if self is a  Array     return self   end end

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Here s a way to deep symbolize an object  def symbolize obj      return obj inject      memo  k v   memo k to sym     symbolize v   memo  if obj is a  Hash     return obj inject      memo v      memo            lt  lt  symbolize v   memo  if obj is a  Array     return obj end

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Similar to previous solutions but written a bit differently    This allows for a hash that is nested and or has arrays  Get conversion of keys to a string as a bonus  Code does not mutate the hash been passed in   module HashUtils   def symbolize keys hash      transformer function   - gt  key    key to sym       transform keys hash  transformer function    end    def stringify keys hash      transformer function   - gt  key    key to s       transform keys hash  transformer function    end    def transform keys obj  transformer function      case obj     when Array       obj map  value  transform keys value  transformer function       when Hash       obj each with object     do   key  value   hash          hash transformer function call key     transform keys value  transformer function        end     else       obj     end   end end

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This is my one liner for nested hashes  def symbolize keys hash    hash each with object         k  v   h  h k to sym    v is a  Hash    symbolize keys v    v   end

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If you are using json  and want to use it as a hash  in core Ruby you can do it   json obj   JSON parse json str  symbolize names  true    symbolize names  If set to true  returns symbols for the names  keys  in a JSON object  Otherwise strings are returned  Strings are the default   Doc  Json parse symbolize names

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Here s a better method  if you re using Rails   params symbolize keys  The end   If you re not  just rip off their code  it s also in the link    myhash keys each do  key    myhash  key to sym rescue key     key    myhash delete key  end

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You could be lazy  and wrap it in a lambda   my hash   YAML load file  yml   my lamb   lambda    key  my hash key to s     my lamb  a     my hash  a      gt  true   But this would only work for reading from the hash - not writing   To do that  you could use Hash merge  my hash   Hash new    h k  h k    h k to s    merge YAML load file  yml      The init block will convert the keys one time on demand  though if you update the value for the string version of the key after accessing the symbol version  the symbol version won t be updated   irb gt  x      a    gt  1   b    gt  2      gt    a   gt 1   b   gt 2  irb gt  y   Hash new    h k  h k    h k to s    merge x     gt    a   gt 1   b   gt 2  irb gt  y  a     the key  a doesn t exist for y  so the init block is called    gt  1 irb gt  y    gt    a   gt 1   a  gt 1   b   gt 2  irb gt  y  a     the key  a now exists for y  so the init block is isn t called    gt  1 irb gt  y  a     3    gt  3 irb gt  y    gt    a   gt 3   a  gt 1   b   gt 2    You could also have the init block not update the hash  which would protect you from that kind of error  but you d still be vulnerable to the opposite - updating the symbol version wouldn t update the string version   irb gt  q      c    gt  4   d    gt  5      gt    c   gt 4   d   gt 5  irb gt  r   Hash new    h k  h k to s    merge q     gt    c   gt 4   d   gt 5  irb gt  r  c    init block is called    gt  4 irb gt  r    gt    c   gt 4   d   gt 5  irb gt  r  c    init block is called again  since this key still isn t in r    gt  4 irb gt  r  c    7    gt  7 irb gt  r    gt    c  gt 7   c   gt 4   d   gt 5    So the thing to be careful of with these is switching between the two key forms   Stick with one

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symbolize keys recursively for any hash   class Hash   def symbolize keys     self is a  Hash    Hash  self map    k v   k respond to   to sym    k to sym   k  v is a  Hash    v symbolize keys   v        self   end end

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How about this   my hash   HashWithIndifferentAccess new YAML load file  yml       my hash  key     gt   val    my hash  key     gt   val

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In Rails you can use     g   gt   a   2   gt    v    gt   b    x    gt     z    gt   c     deep symbolize keys    Converts to     g  gt  a   2  gt   v  gt  b    x  gt   z  gt  c

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params symbolize keys will also work  This method turns hash keys into symbols and returns a new hash

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This is for people who uses mruby and do not have any symbolize keys method defined   class Hash   def symbolize keys      self keys each do  k        if self k  is a  Hash         self k  symbolize keys        end       if k is a  String         raise RuntimeError   Symbolizing key    k   means overwrite some data  key    k  exists   if self k to sym          self k to sym    self k          self delete k        end     end     return self   end end   The method    symbolizes only keys that are String if symbolize a string means to lose some informations  overwrite part of hash  raise a RuntimeError symbolize also recursively contained hashes return the symbolized hash works in place

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I really like the Mash gem   you can do mash  key    or mash  key   or mash key

[ruby] Best way to convert strings to symbols in hash

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