Merge the value of same key names in ruby on rails - ruby-on-rails

Question

I want to merge the ids of same name values
hashes = [{
id: 3456824,
name: 'John'
},{
id: 6578954,
name: 'Vicky'
},{
id: 987456,
name: 'John'
}]
Expected:
[{
id: [3456824,987456],
name: 'John'
},{
id: 6578954,
name: 'Vicky'
}]
how I can achieve this in ruby on rails?

Answer 1

Here is a one liner:
hashes = [{
id: 3456824,
name: 'John'
},{
id: 6578954,
name: 'Vicky'
},{
id: 987456,
name: 'John'
}]
result = hashes.group_by{|h| h[:name] }.map{|k, v| {id: v.map{|x| x[:id]}, name: k}}
puts result
Check this repl: https://repl.it/repls/ShadowyCornyVideogames

Answer 2

Here are two ways to compute the desired result.
Use the form of Hash::new that takes a block
hashes.each_with_object(Hash.new { |h,k| h[k] = [] }) do |g,h|
h[g[:name]] << g[:id]
end.map { |name,id| { id: id, name: name } }
#=> [{:id=>[3456824, 987456], :name=>"John"},
# {:id=>[6578954], :name=>"Vicky"}]
The first step of this calculation1 is
hashes.each_with_object(Hash.new { |h,k| h[k] = [] }) do |g,h|
h[g[:name]] << g[:id]
end
#=> {"John"=>[3456824, 987456], "Vicky"=>[6578954]}
If a hash is defined
h = Hash.new { |h,k| h[k] = [] }
and (possibly after having added key-value pairs) h has no key k, h[k] in
h[k] << v
causes the block { |h,k| h[k] = [] } to be executed, resulting in the key value pair k=>[] being added to h, then << v is executed, changing h[k] from [] to [k].
Notice that this returns :id=>[6578954], rather than :id=>6578954, which was asked for by the question. Having all values of :id return an array avoids the need to check if :id returns an array or integer in subsequent code that processes the return value of this operation.
If :id=>6578954, were desired, one could write
hashes.each_with_object(Hash.new { |h,k| h[k] = [] }) do |g,h|
h[g[:name]] << g[:id]
end.transform_values { |v| v.size==1 ? v.first : v }.
map { |name,id| { id: id, name: name } }
#=> [{:id=>[3456824, 987456], :name=>"John"},
# {:id=>6578954, :name=>"Vicky"}]
See Hash#transform_values.
Use the form of Hash#update (a.k.a. merge!) that employs a block to determine the values of keys that are present in both hashes being merged
arr.each_with_object({}) do |g,h|
h.update(g[:name]=>[g[:id]]) { |_,o,n| o+n }
end.map { |name,id| { id: id, name: name } }
#=> [{:id=>[3456824, 987456], :name=>"John"},
# {:id=>[6578954], :name=>"Vicky"}]
If :id=>6578954, rather than :id=>[6578954], were desired:
arr.each_with_object({}) do |g,h|
h.update(g[:name]=>g[:id]) { |_,o,n| [*o,n] }
end.map { |name,id| { id: id, name: name } }
#=> [{:id=>[3456824, 987456], :name=>"John"},
# {:id=>6578954, :name=>"Vicky"}]
Notice that here update's argument is g[:name]=>g[:id] whereas it was previously g[:name]=>[g[:id]].
The first step is as follows.
arr.each_with_object({}) do |g,h|
h.update(g[:name]=>g[:id]) { |_,o,n| [*o,n] }
end
#=> {"John"=>[3456824, 987456], "Vicky"=>6578954}
In general, one or both of these approaches can be taken when Enumerable#group_by can be used. The reverse if often true also. The choice among these methods is a matter of personal taste.
1. A variant of the first part of this calculation is hashes.each_with_object({}) { |g,h| (h[g[:name]] ||= []) << g[:id] } #=> {"John"=>[3456824, 987456], "Vicky"=>[6578954]}.

Answer 3

You can do it like this:
args = [{
id: 3456824,
name: 'John'
},{
id: 6578954,
name: 'Vicky'
},{
id: 987456,
name: 'John'
}]
value_pairs = args.map { |h| h.values_at(:name, :id) }
grouped_by_name = value_pairs.group_by(&:first).transform_values { |arr| arr.map(&:last) }
as_hashes = grouped_by_name.map { |name, ids| { id: ids, name: name } }

Answer 4

One more possible solution is:
array = [
{
id: 3456824,
name: "John"
},
{
id: 6578954,
name: "Vicky"
},
{
id: 987456,
name: "John"
}
]
grouped_by_name = array.each_with_object(Hash.new {|h,k| h[k] = [] }) do |hash, result|
result[hash[:name]] << hash[:id]
end
=> {"John"=>[3456824, 987456], "Vicky"=>[6578954]}
grouped_by_name.map do |grouped_hash|
{
id: grouped_hash.last,
name: grouped_hash.first
}
end
=> [{:id=>[3456824, 987456], :name=>"John"}, {:id=>[6578954], :name=>"Vicky"}]