How to use ruby uniq on nested array/hash - ruby-on-rails

Question

I am trying to call the uniq method on the follow json so that it would only return unique result base on employee_id
# Json array
a ={
results: [
{
employee: {
name: "A",
employee_id: "A-00016",
title: 1
}
},{
employee: {
name: "A",
employee_id: "A-00016",
title: 2
}
},{
employee: {
name: "C",
employee_id: "C-00017",
title: 3
}
}
]
}
# Calling uniq on a
a.uniq { |p| p.values_at(:employee_id) }
However, I am only getting this result
{
results: [
{
employee: {
name: "A",
employee_id: "A-00016",
title: 1
}
}
]
}
Instead of what I want
{
results: [
{
employee: {
name: "A",
employee_id: "A-00016",
title: 1
},{
employee: {
name: "C",
employee_id: "C-00017",
title: 3
}
}
]
}
Am I using the correct method to output the result I want?

Answer 1

With uniq:
input[:results].uniq { |e| e[:employee][:employee_id] }
#⇒ [
# {:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>"1"}},
# {:employee=>{:name=>"C", :employee_id=>"C-00017", :title=>"3"}}]
But I believe there should be some condition applied on what to choose from siblings having the same id. The code below selects the one, having max title value:
input[:results].group_by { |e| e[:employee][:employee_id] }
.map { |_, v| v.max_by { |e| e[:employee][:title].to_i } }
#⇒ [
# {:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>"2"}},
# {:employee=>{:name=>"C", :employee_id=>"C-00017", :title=>"3"}}]

Answer 2

Here is one way to do this, in order to return the modified input hash, we can use uniq! which will modify the array a[:results] in place. We use dup to duplicate the hash a to preserve it, and then use tap to operate on duplicated hash.
r = a.dup.tap do |h|
h[:results].uniq! do |h|
h[:employee][:employee_id]
end
end
#=> {:results=>
# [
# {:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>1}},
# {:employee=>{:name=>"C", :employee_id=>"C-00017", :title=>3}}
# ]
# }

Answer 3

def selection_criterion(h)
h[:title].to_i
end
{results: a[:results].group_by {|h| h[:employee][:employee_id]}.
values.
map {|arr| arr.max_by {|h| selection_criterion(h[:employee])}}}
#=> {:results=>
# [{:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>2}},
# {:employee=>{:name=>"C", :employee_id=>"C-00017", :title=>3}}]}
Define selection_criterion as desired, and possible change max_by to min_by.
The steps are as follows.
b = a[:results]
# => [{:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>1}},
# {:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>2}},
# {:employee=>{:name=>"C", :employee_id=>"C-00017", :title=>3}}]
c = b.group_by { |h| h[:employee][:employee_id] }
#=> {"A-00016"=>[{:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>1}},
# {:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>2}}],
# "C-00017"=>[{:employee=>{:name=>"C", :employee_id=>"C-00017", :title=>3}}]}
d = c.values
#=> [[{:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>1}},
# {:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>2}}],
# [{:employee=>{:name=>"C", :employee_id=>"C-00017", :title=>3}}]]
e = d.map { |arr| arr.max_by { |h| selection_criterion(h[:employee]) } }
#=> [{:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>2}},
# {:employee=>{:name=>"C", :employee_id=>"C-00017", :title=>3}}]
{ results: e }
#=> {:results=>
# [{:employee=>{:name=>"A", :employee_id=>"A-00016", :title=>2}},
# {:employee=>{:name=>"C", :employee_id=>"C-00017", :title=>3}}]}