How to remove a key from Hash and get the remaining hash in Ruby Rails

Question

To add a new pair to Hash I do     a   gt  1   b   gt  2  merge    c   gt  3        gt    a   gt  1   b   gt  2   c   gt  3    Is there a similar way to delete a key from Hash    This works     a   gt  1   b   gt  2  reject     k  k     a        gt    b   gt  2    but I would expect to have something like     a   gt  1   b   gt  2  delete   a       gt    b   gt  2    It is important that the returning value will be the remaining hash  so I could do things like   foo my hash reject     k  k    my key      in one line

User · Answer

There are many ways to remove a key from a hash and get the remaining hash in Ruby.

.slice => It will return selected keys and not delete them from the original hash. Use slice! if you want to remove the keys permanently else use simple slice.

2.2.2 :074 > hash = {"one"=>1, "two"=>2, "three"=>3}
 => {"one"=>1, "two"=>2, "three"=>3} 
2.2.2 :075 > hash.slice("one","two")
 => {"one"=>1, "two"=>2} 
2.2.2 :076 > hash
 => {"one"=>1, "two"=>2, "three"=>3}

.delete => It will delete the selected keys from the original hash(it can accept only one key and not more than one).

2.2.2 :094 > hash = {"one"=>1, "two"=>2, "three"=>3}
 => {"one"=>1, "two"=>2, "three"=>3} 
2.2.2 :095 > hash.delete("one")
 => 1 
2.2.2 :096 > hash
 => {"two"=>2, "three"=>3}

.except => It will return the remaining keys but not delete anything from the original hash. Use except! if you want to remove the keys permanently else use simple except.

2.2.2 :097 > hash = {"one"=>1, "two"=>2, "three"=>3}
 => {"one"=>1, "two"=>2, "three"=>3} 
2.2.2 :098 > hash.except("one","two")
 => {"three"=>3} 
2.2.2 :099 > hash
 => {"one"=>1, "two"=>2, "three"=>3}

.delete_if => In case you need to remove a key based on a value. It will obviously remove the matching keys from the original hash.

2.2.2 :115 > hash = {"one"=>1, "two"=>2, "three"=>3, "one_again"=>1}
 => {"one"=>1, "two"=>2, "three"=>3, "one_again"=>1} 
2.2.2 :116 > value = 1
 => 1 
2.2.2 :117 > hash.delete_if { |k,v| v == value }
 => {"two"=>2, "three"=>3} 
2.2.2 :118 > hash
 => {"two"=>2, "three"=>3}

.compact => It is used to remove all nil values from the hash. Use compact! if you want to remove the nil values permanently else use simple compact.

2.2.2 :119 > hash = {"one"=>1, "two"=>2, "three"=>3, "nothing"=>nil, "no_value"=>nil}
 => {"one"=>1, "two"=>2, "three"=>3, "nothing"=>nil, "no_value"=>nil} 
2.2.2 :120 > hash.compact
 => {"one"=>1, "two"=>2, "three"=>3}

Results based on Ruby 2.2.2.

User · Answer

in pure Ruby     a   gt  1   b   gt  2  tap  x  x delete  a         gt    b  gt 2

User · Answer

Oneliner plain ruby  it works only with ruby   1 9 x   1 9 3p0  002  gt  h     a   gt  1   b   gt  2     gt    a  gt 1   b  gt 2   1 9 3p0  003  gt  h tap    hs  hs delete  a       gt    b  gt 2     Tap method always return the object on which is invoked     Otherwise if you have required active support core ext hash  which is automatically required in every Rails application  you can use one of the following methods depending on your needs         irb 1 9 3p125  001  gt  require  active support core ext hash    gt  true  1 9 3p125  002  gt  h     a   gt  1   b   gt  2   c   gt  3     gt    a  gt 1   b  gt 2   c  gt 3   1 9 3p125  003  gt  h except  a     gt    b  gt 2   c  gt 3   1 9 3p125  004  gt  h slice  a     gt    a  gt 1     except uses a blacklist approach  so it removes all the keys listed as args  while slice uses a whitelist approach  so it removes all keys that aren t listed as arguments  There also exist the bang version of those method  except  and slice   which modify the given hash but their return value is different both of them return an hash  It represents the removed keys for slice  and the keys that are kept for the except    1 9 3p125  011  gt    a   gt  1   b   gt  2   c   gt  3  except   a     gt    b  gt 2   c  gt 3   1 9 3p125  012  gt    a   gt  1   b   gt  2   c   gt  3  slice   a     gt    b  gt 2   c  gt 3

User · Answer

See Ruby on Rails  Delete multiple hash keys  hash delete if   k   keys to delete include  k

User · Answer

Instead of monkey patching or needlessly including large libraries  you can use refinements if you are using Ruby 2   module HashExtensions   refine Hash do     def except   candidates        candidates each    candidate  delete candidate          self     end      def except  candidates        dup remove  candidates      end   end end   You can use this feature without affecting other parts of your program  or having to include large external libraries   class FabulousCode   using HashExtensions    def incredible stuff     delightful hash except  not fabulous key    end end

User · Answer

If you want to use pure Ruby  no Rails   don t want to create extension methods  maybe you need this only in one or two places and don t want to pollute namespace with tons of methods  and don t want to edit hash in place  i e   you re fan of functional programming like me   you can  select     gt  gt  x     a   gt  1   b   gt  2   c   gt  3    gt    a  gt 1   b  gt 2   c  gt 3   gt  gt  x select  x  x     a    gt    b  gt 2   c  gt 3   gt  gt  x select  x     a   b  include  x     gt    c  gt 3   gt  gt  x   gt    a  gt 1   b  gt 2   c  gt 3

User · Answer

This is a one line way to do it  but it s not very readable  Recommend using two lines instead   use remaining hash for something Proc new   hash delete  key   hash   call

User · Answer

in lib core extensions rb class Hash    pass single or array of keys  which will be removed  returning the remaining hash   def remove   keys      keys each  key  self delete key        self   end     non-destructive version   def remove  keys      self dup remove   keys    end end   in config initializers app environment rb  or anywhere in config initializers  require  core extensions    I ve set this up so that  remove returns a copy of the hash with the keys removed  while remove  modifies the hash itself   This is in keeping with ruby conventions   eg  from the console   gt  gt  hash     a   gt  1   b   gt  2    gt    b  gt 2   a  gt 1   gt  gt  hash remove  a    gt    b  gt 2   gt  gt  hash   gt    b  gt 2   a  gt 1   gt  gt  hash remove   a    gt    b  gt 2   gt  gt  hash   gt    b  gt 2   gt  gt  hash remove   a   b    gt

User · Answer

Multiple ways to delete Key in Hash  you can use any Method from below  hash    a  1  b  2  c  3  hash except   a    Will remove  a  and return HASH hash   Output  -  b  2  c  3   hash    a  1  b  2  c  3  hash delete  a    will remove  a  and return 1 if  a  not present than return nil   So many ways is there  you can look on Ruby doc of Hash here   Thank you

User · Answer

Why not just use   hash delete key

User · Answer

This would also work  hash hey    nil

User · Answer

Rails has an except except  method that returns the hash with those keys removed  If you re already using Rails  there s no sense in creating your own version of this    class Hash     Returns a hash that includes everything but the given keys        hash     a  true  b  false  c  nil        hash except  c      gt    a  true  b  false        hash     gt    a  true  b  false  c  nil          This is useful for limiting a set of parameters to everything but a few known toggles         person update params  person  except  admin     def except  keys      dup except   keys    end      Replaces the hash without the given keys        hash     a  true  b  false  c  nil        hash except   c      gt    a  true  b  false        hash     gt    a  true  b  false     def except   keys      keys each    key  delete key        self   end end

User · Answer

It s was great if delete return the delete pair of the hash  I m doing this   hash    a  1  b  2  c  3   b  hash delete  b       gt    b  gt 2  hash      gt    a  gt 1   c  gt 3

User · Answer

You can use except  from the facets gem    gt  gt  require  facets    or require  facets hash except    gt  true  gt  gt    a   gt  1   b   gt  2  except  a    gt    b  gt 2    The original hash does not change   EDIT  as Russel says  facets has some hidden issues and is not completely API-compatible with ActiveSupport  On the other side ActiveSupport is not as complete as facets  In the end  I d use AS and let the edge cases in your code

User · Answer

Hash except  Ruby 3 0   Starting from Ruby 3 0  Hash except is a build-in method  As a result  there is no more need to depend on ActiveSupport or write monkey-patches in order to use it  h     a  1  b  2  c  3   p h except  a     gt    b  gt 2   c  gt 3   Sources   Hash except from official Ruby docs  Link to the PR  Ruby 3 0 adds Hash except and ENV except

[ruby-on-rails] How to remove a key from Hash and get the remaining hash in Ruby/Rails?

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