How do I compare two hashes

Question

I am trying to compare two Ruby Hashes using the following code      usr bin env ruby  require  yaml  require  active support   file1   YAML  load File open    en 20110207 yml    file2   YAML  load File open    locales en yml     arr       file1 select    k v    file2 select    k2  v2      arr  lt  lt     v2   if    v         v2          puts arr   The output to the screen is the full file from file2  I know for a fact that the files are different  but the script doesn t seem to pick it up

User · Answer

You can try the hashdiff gem  which allows deep comparison of hashes and arrays in the hash   The following is an example   a    a  x 2  y 3  z 4   b  x 3  z 45   b    a  y 3   b  y 3  z 30    diff   HashDiff diff a  b  diff should       -    a x   2     -    a z   4     -    b x   3          b z   45  30          b y   3

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If you want to get what is the difference between two hashes  you can do this   h1     a   gt  20   b   gt  10   c   gt  44  h2     a   gt  2   b   gt  10   c   gt   44   result      h1 each   k  v  result k    h2 k  if h2 k     v   p result    gt    a   gt  2   c   gt   44

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and now in module form to be applied to a variety of collection classes  Hash among them    It s not a deep inspection  but it s simple     Enable  diffing  and two-way transformations between collection objects module Diffable     Calculates the changes required to transform self to the given collection       param b  Enumerable  The other collection object      return  Array  The Diff  A two-element change set representing items to exclude and items to include   def diff  b       a  b   to a  b to a      a - b  b - a    end      Consume return value of Diffable diff to produce a collection equal to the one used to produce the given diff       param to drop  Enumerable  items to exclude from the target collection      param to add   Enumerable  items to include in the target collection      return  Array  New transformed collection equal to the one used to create the given change set   def apply diff  to drop  to add       to a - to drop   to add   end end  if   FILE       0     Demo  Hashes with overlapping keys and somewhat random values    Hash send  include  Diffable   rng   Random new   a     a   q  to a reduce Hash     h k  h merge  Hash k  rng rand 2       b     i   z  to a reduce Hash     h k  h merge  Hash k  rng rand 2       raise unless a    Hash  b apply diff  b diff a       change b to a   raise unless b    Hash  a apply diff  a diff b       change a to b   raise unless a    Hash  a apply diff  a diff a       change a to a   raise unless b    Hash  b apply diff  b diff b       change b to b end

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I developed this to compare if two hashes are equal  def hash equal  hash1  hash2    array1   hash1 to a   array2   hash2 to a    array1 - array2   array2 - array1        end   The usage    gt  hash equal   a  4    a  4     gt  true  gt  hash equal   a  4    b  4     gt  false   gt  hash equal   a   b  3     a   b  3      gt  true  gt  hash equal   a   b  3     a   b  4      gt  false   gt  hash equal   a   b   c   d   e   f   g   h  1           a   b   c   d   e   f   g   h  1            gt  true  gt  hash equal   a   b   c   d   e   f   g   marino  1           a   b   c   d   e   f   g   h  2            gt  false

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what about convert both hash to json and compare as string  but keeping in mind that  require  json  h1    a  20  h2    a   20    h1 to json  h1 to json   gt  true h1 to json  h2 to json   gt  false

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I had the same problem and sent a pull request to rails   Works with deeply nested hash Works with arrays of hashes   https   github com elfassy rails commit 5f3410e04fe8c4d4745397db866c9633b80ccec6

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Rails is deprecating the diff method   For a quick one-liner   hash1 to s    hash2 to s

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If you want a nicely formatted diff  you can do this     Gemfile gem  awesome print    or gem install awesome print   And in your code   require  ap   def my diff a  b    as   a ai plain  true  split   n   map  amp  strip    bs   b ai plain  true  split   n   map  amp  strip      as - bs     bs - as   join   n   end  puts my diff  foo   bar  nested   val1  1  val2  2   end   v                 foo   bar  n2   nested   val1  1  val2  3    end   v     The idea is to use awesome print to format  and diff the output  The diff won t be exact  but it is useful for debugging purposes

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How about another  simpler approach   require  fileutils  FileUtils cmp file1  file2

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You can compare hashes directly for equality   hash1     a    gt  1   b    gt  2  hash2     a    gt  1   b    gt  2  hash3     a    gt  1   b    gt  2   c    gt  3   hash1    hash2     gt  true hash1    hash3     gt  false  hash1 to a    hash2 to a     gt  true hash1 to a    hash3 to a     gt  false       You can convert the hashes to arrays  then get their difference   hash3 to a - hash1 to a     gt     c   3    if  hash3 size  gt  hash1 size    difference   hash3 to a - hash1 to a else   difference   hash1 to a - hash3 to a end Hash  difference flatten      gt    c   gt 3      Simplifying further   Assigning difference via a ternary structure     difference    hash3 size  gt  hash1 size                      hash3 to a - hash1 to a                     hash1 to a - hash3 to a   gt     c   3     Hash  difference flatten     gt    c   gt 3    Doing it all in one operation and getting rid of the difference variable     Hash       hash3 size  gt  hash1 size               hash3 to a - hash1 to a           hash1 to a - hash3 to a     flatten     gt    c   gt 3

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Here is algorithm to deeply compare two Hashes  which also will compare nested Arrays         HashDiff new         val  1  nested    a 1    b   1  2              val  2  nested    a 1    b   1            report     Output  val  - 1   2 nested  gt  1  gt  b  gt  1  - 2   Implementation   class HashDiff    attr reader  left   right    def initialize left  right  config       path   nil       left    left      right   right      config   config      path   path      conformity   0   end    def conformity     find differences      conformity   end    def report      config  report    true     find differences   end    def find differences     if hash  left   amp  amp  hash  right        compare hashes keys     elsif left is a  Array   amp  amp  right is a  Array        compare arrays     else       report diff     end   end    def compare hashes keys     combined keys each do  key        l   value with default left  key        r   value with default right  key        if l    r          conformity    100       else         compare sub items l  r  key       end     end   end    private    def compare sub items l  r  key      diff   self class new l  r   config  path key        conformity    diff conformity   end    def report diff     return unless  config  report       puts     path        puts  -   left   unless left    NO VALUE     puts      right   unless right    NO VALUE   end    def combined keys      left keys   right keys  uniq   end    def hash  value      value is a  Hash    end    def compare arrays     l  r   left clone  right clone     l each with index do  l item  l index        max item index   nil       max conformity   0       r each with index do  r item  i          if l item    r item            conformity    1           r i    TAKEN           break         end          diff   self class new l item  r item              c   diff conformity         if c  gt  max conformity           max conformity   c           max item index   i         end       end or next        if max item index         key   l index    max item index   l index      l index    max item index           compare sub items l item  r max item index   key         r max item index    TAKEN       else         compare sub items l item  NO VALUE  l index       end     end      r each with index do  item  index        compare sub items NO VALUE  item  index unless item    TAKEN     end   end    def path key      p       path   gt    if  path        p   key     end    def value with default obj  key      obj fetch key  NO VALUE    end    module NO VALUE  end   module TAKEN  end  end

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You could use a simple array intersection  this way you can know what differs in each hash       hash1     a  1   b  2       hash2     a  2   b  2        overlapping elements   hash1 to a  amp  hash2 to a      exclusive elements from hash1   hash1 to a - overlapping elements     exclusive elements from hash2   hash2 to a - overlapping elements

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This was answered in  Comparing ruby hashes   Rails adds a diff method to hashes  It works well

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If you need a quick and dirty diff between hashes which correctly supports nil in values you can use something like  def diff one  other     one keys   other keys  uniq inject     do  memo  key      unless one key  key   amp  amp  other key  key   amp  amp  one key     other key        memo key     one key  key    one key      no key  other key  key    other key      no key      end     memo   end end

[ruby] How do I compare two hashes?

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