Difference between update(other_hash) and merge(other_hash)

ruby hash#merge
ruby merge two hashes with same keys
ruby merge multiple hashes
ruby hash select
ruby hash#fetch
rails hash
ruby hash map
ruby hash deep merge

Update Code:

irb(main):001:0> h1 = { "a" => 100, "b" => 200 }
=> {"a"=>100, "b"=>200}
irb(main):002:0> h2 = { "b" => 254, "c" => 300 }
=> {"b"=>254, "c"=>300}
irb(main):003:0> h1.update(h2)
=> {"a"=>100, "b"=>254, "c"=>300}

Merge Code:

irb(main):001:0> h1 = { "a" => 100, "b" => 200 }
=> {"a"=>100, "b"=>200}
irb(main):002:0> h2 = { "b" => 254, "c" => 300 }
=> {"b"=>254, "c"=>300}
irb(main):003:0> h1.merge(h2)
=> {"a"=>100, "b"=>254, "c"=>300}
irb(main):004:0>

I ran the above merge and update method on the same hash. But got the same output. So here my question is: are update and merge works with same logic? if not same then how the output came same for those?

Are update and merge works with same logic?

No, they are not the same. update is an alias for merge!, which is the in-place variant of merge.

if not same then how the output came same for those?

Because in both cases you are using the return value of the call, however, the value of h1 is different in each case:

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 254, "c" => 300 }
h1.update(h2)
h1  #=> { "a" => 100, "b" => 254, "c" => 300 }

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 254, "c" => 300 }
h1.merge(h2)
h1  #=> { "a" => 100, "b" => 200 }

merge! (Hash), Returns a new hash containing the contents of other_hash and the contents of hsh. If no block is specified, the value for entries with duplicate keys will be that of � Merge join requires that both inputs be in memory (as opposed to a hash join, where only the smaller input is in memory). Hash join has a substantial advantage over merge join only. In fact, a query processor using only merge join for large inputs is 40% slower than one using hash join (30 vs. 42).

Hash#update is an alias for Hash#merge! http://ruby-doc.org/core-1.9.3/Hash.html#method-i-update

merge (Hash), A Hash is a dictionary-like collection of unique keys and their values. Also called associative merge(other_hash){|key, oldval, newval| block} → new_hash. Returns a new hash once for every key. This method does not change the values. * The big idea of hash join is to use a temporary hash table as a “lookup index”. The inner or target table has column values that pass any previous filters put into the hash table, and column values from the outer table are looked up in the hash

Hash#update is alias to Hash#merge!

The difference between Hash#merge and Hash#update is Hash#update updates keys/values in-place, whereas Hash#merge returns updated hash without touching the calling instance.

Class: Hash (Ruby 2.5.1), update(other_hash) Link. Updates the receiver in-place, merging in the hash passed as argument: hash_1 = ActiveSupport::HashWithIndifferentAccess.new� Facilitating Merge Joins. To facilitate a merge join, create projections for the joined tables that are sorted on the join predicate columns. The join predicate columns should be the first columns in the ORDER BY clause. For example, tables first and second are defined as follows, with projections first_p1 and second_p1, respectively.

h1.update(h2) - updates h1 instance - returns updated h1; h1.merge(h2) - leaves h1 and creates updated copy - returns a updated copy of h1 (h3 I could call it)

ActiveSupport::HashWithIndifferentAccess, subject hash (self). As you'd expect at Inn Style — a tool for accommodation owners to… Returns a new hash with self and other_hash merged recursively. So let's change that line to use our new friend deep_merge . Hash#merge!() : merge!() is a Hash class method which can add the content the given hash array to the other. Entries with duplicate keys are overwritten with the values from each other_hash successively if no block is given. Syntax: Hash.merge!() Parameter: Hash values. Return: add the content the given hash array to the other. Example #1 :

Object::HashWithIndifferentAccess, class Hash. A Hash is a dictionary-like collection of unique keys and their values. merge(other_hash){|key, oldval, newval| block} → new_hash. Returns a new� It choose many times merge join when it should use hash join, one example is one of the batch jobs running in 9.2.0.4 used to take 8 hours, now it takes 45 minutes. All we did were forcing it to use hash join instead of merge join, which CBO thought was the best

Merge and Deep Merge — and Why One Day You'll Find The Latter , Hash array Although similar, but there is a very important distinction: Hash elements are in no hash.merge (other_hash) {| key, oldval, newval | block} Returns� Teams. Q&A for Work. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

class Hash - Documentation for Ruby 2.0.0, Ruby - Hashes - A Hash is a collection of key-value pairs like this: employee = > salary. It is similar to an Array, hash.merge(other_hash) { |key, oldval, newval| block }. Returns a new hash array to a string. 39. hash.update(other_hash) [or]. If no block is given, entries with duplicate keys are overwritten with the values from each other_hash successively, otherwise the value for each duplicate key is determined by calling the block with the key, its value in the receiver and its value in each other_hash. When called without any argument, returns a copy of the receiver.

Comments
  • h1.update(h2) and h1.merge!(h2) are same i just tested.
  • Actually it's an alias for merge! which updates the current hash, merge returns a copy
  • @aromero Of course, without your edit, the original answer is completely incorrect.
  • @AndrewMarshall it's just a bang, feel free to revert the changes