Changing every value in a hash in Ruby

Question

I want to change every value in a hash so as to add     before and after the value so     a  gt  a     b  gt  b      must be changed to     a  gt   a      b  gt   b       What s the best way to do this

User · Answer

Ruby 2 4 introduced the method Hash transform values   which you could use      a  gt  a     b  gt  b    transform values     v      v          gt    a  gt   a     b  gt   b

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After testing it with RSpec like this   describe Hash do   describe  map values do     it  should map the values  do       expect   a   gt  2   b   gt  3  map values    x  x    2    to eq   a   gt  4   b   gt  9       end   end end   You could implement Hash map values as follows   class Hash   def map values     Hash map    k  v   k  yield v        end end   The function then can be used like this     a  gt  a     b  gt  b   map values    v      v          a  gt   a     b  gt   b

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If you want the actual strings themselves to mutate in place  possibly and desirably affecting other references to the same string objects      Two ways to achieve the same result  any Ruby version  my hash each     str  str gsub               my hash each     str  str replace     str        If you want the hash to change in place  but you don t want to affect the strings  you want it to get new strings      Two ways to achieve the same result  any Ruby version  my hash each   key str  my hash key        str      my hash inject my hash    h  k str   h k      str     h     If you want a new hash     Ruby 1 8 6  new hash   Hash  my hash map  k str   k     str       flatten     Ruby 1 8 7  new hash   Hash my hash map  k str   k     str

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my hash each do  key  value    my hash key        value    end

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In Ruby 2 1 and higher you can do    a   a   b   b    map    k  str   k      str       to h

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If you are curious which inplace variant is the fastest here it is   Calculating ------------------------------------- inplace transform values  1 265k     0 7   i s -      6 426k in   5 080305s       inplace update      1 300k     2 7   i s -      6 579k in   5 065925s   inplace map reduce    281 367      1 1   i s -      1 431k in   5 086477s       inplace merge       1 305k     0 4   i s -      6 630k in   5 080751s         inplace each      1 073k     0 7   i s -      5 457k in   5 084044s       inplace inject    697 178      0 9   i s -      3 519k in   5 047857s

User · Answer

Hash merge  is the cleanest solution  o     a   a   b   b    o merge  o     key  value       value        puts o inspect  gt     a   gt    a     b   gt    b

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The best way to modify a Hash s values in place is  hash update hash      v      v        Less code and clear intent  Also faster because no new objects are allocated beyond the values that must be changed

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One method that doesn t introduce side-effects to the original   h     a   gt   a    b   gt   b   h2   Hash h map   k v   k        v            Hash map may also be an interesting read as it explains why the Hash map doesn t return a Hash  which is why the resultant Array of  key value  pairs is converted into a new Hash  and provides alternative approaches to the same general pattern   Happy coding    Disclaimer  I am not sure if Hash map semantics change in Ruby 2 x

User · Answer

A bit more readable one  map it to an array of single-element hashes and reduce that with merge  the hash map   key value   key   gt      value       reduce  merge

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There is a new  Rails way  method for this task    http   api rubyonrails org classes Hash html method-i-transform values

[ruby] Changing every value in a hash in Ruby

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