How to add to an existing hash in Ruby

Question

In regards to adding an key   gt  value pair to an existing populated hash in Ruby   I m in the process of working through Apress  Beginning Ruby and have just finished the hashes chapter   I am trying to find  the simplest way to achieve the same results with hashes as this does with arrays   x    1  2  3  4  x  lt  lt  5 p x

User · Answer

hash    hash  a     a  hash  b     b  hash     a   gt   a     b    gt  b    You might get your key and value from user input  so you can use Ruby  to sym  can convert a string to a symbol  and  to i will convert a string to an integer  For example    movies     movie   gets chomp rating   gets chomp movies movie to sym    rating to int   movie will convert to a symbol as a key in our hash  and    rating will be an integer as a value

User · Answer

my hash     a   gt  5  my hash  key     value

User · Answer

hash     a   a   b   b       gt    a  gt  a    b  gt  b   hash merge   c   c   d   d        gt    a  gt  a    b  gt  b    c  gt  c    d  gt  d      Returns the merged value   hash    gt    a  gt  a    b  gt  b      But doesn t modify the caller object  hash   hash merge   c   c   d   d        gt    a  gt  a    b  gt  b    c  gt  c    d  gt  d    hash    gt    a  gt  a    b  gt  b    c  gt  c    d  gt  d      Reassignment does the trick

User · Answer

If you want to add more than one   hash     a   gt  1   b   gt  2  hash merge   c   gt  3   d   gt  4 p hash

User · Answer

x     ca   gt   Canada    us   gt   United States   x  de     Germany  p x

User · Answer

If you have a hash  you can add items to it by referencing them by key   hash       hash  a     a  hash  a      gt   a    Here  like     creates an empty array      will create a empty hash   Arrays have zero or more elements in a specific order  where elements may be duplicated  Hashes have zero or more elements organized by key  where keys may not be duplicated but the values stored in those positions can be   Hashes in Ruby are very flexible and can have keys of nearly any type you can throw at it  This makes it different from the dictionary structures you find in other languages   It s important to keep in mind that the specific nature of a key of a hash often matters   hash      a   gt   a       Fetch with Symbol  a finds the right value hash  a      gt   a     Fetch with the String  a  finds nothing hash  a       gt  nil    Assignment with the key  b adds a new entry hash  b     Bee     This is then available immediately hash  b      gt   Bee     The hash now contains both keys hash     gt     a   gt   a    b   gt   Bee      Ruby on Rails confuses this somewhat by providing HashWithIndifferentAccess where it will convert freely between Symbol and String methods of addressing   You can also index on nearly anything  including classes  numbers  or other Hashes   hash     Object   gt  true  Hash   gt  false    hash Object      gt  true  hash Hash      gt  false  hash Array      gt  nil   Hashes can be converted to Arrays and vice-versa     Like many things  Hash supports  to a    a   gt   a    to a     gt     a   a       Hash also has a handy Hash   method to create new hashes from arrays Hash    a   a         gt    a  gt  a      When it comes to  inserting  things into a Hash you may do it one at a time  or use the merge method to combine hashes      a   gt   a    merge  b   gt   b       a  gt  a   b  gt  b     Note that this does not alter the original hash  but instead returns a new one  If you want to combine one hash into another  you can use the merge  method   hash      a   gt   a       Returns the result of hash combined with a new hash  but does not alter   the original hash  hash merge  b   gt   b       gt    a  gt  a   b  gt  b      Nothing has been altered in the original hash     gt    a  gt  a      Combine the two hashes and store the result in the original hash merge   b   gt   b       gt    a  gt  a   b  gt  b      Hash has now been altered hash     gt    a  gt  a   b  gt  b     Like many methods on String and Array  the   indicates that it is an in-place operation

User · Answer

You can use double splat operator which is available since Ruby 2 0  h     a  1  b  2   h       h  c  3   p h     gt    a  gt 1   b  gt 2   c  gt 3

[ruby] How to add to an existing hash in Ruby

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