rails array using group + each

Question

Question: How can I make a grouped array like this?

event_id: 1, person_id: 1, tasks: [1, 2] 
event_id: 1, person_id: 2, tasks: [3] 
event_id: 2, person_id: 1, tasks: [4]

The givens:

Tasks table:

Event.rb:

has_many :tasks
has_many :people

Task.rb

belongs_to :event

Person.rb

belongs_to :event

My thoughts are to do something like this (doesn't work):

- @grouped_tasks = Task.all.group(:event_id, :person_id).each do |z|
  = z.event.id
  = z.member.id
  = z.tasks.collect{|r| r.task.name}.join(",")
  = z.tasks.pluck(:name)

What exactly you want is unclear. You want an array or a table or what? Just write down what you want as final product for 2 3 tasks. I think it is not complicated. — ARK
– ARK, Commented Jan 17, 2020 at 19:37
I'd use an has_and_belongs_to_many or an has_many :through association. You find out which to pick here. — 3limin4t0r
– 3limin4t0r, Commented Jan 17, 2020 at 19:39
@ARK - I want a table grouped like event_id: 1, person_id: 1, tasks: [1, 2] — Yshmarov
– Yshmarov, Commented Jan 17, 2020 at 19:41
Please replace the "task table" with a Ruby object that readers can cut-and-paste to test code. Same with the array of hashes: arr = [{ event_id: 1, person_id: 1, tasks: [1, 2]}, {...}, {...}]. Notice that I assigned a variable (arr) to that array. That way readers can refer to that variable in answers and comments without having to define it. Please also assign a variable to the task table object. In general, do not use pictures of code or data. — Cary Swoveland
– Cary Swoveland, Commented Jan 17, 2020 at 20:48

3limin4t0r · Accepted Answer · 2020-01-17 20:23:49Z

2

Instead of using an SQL "GROUP BY" with group(:event_id, :person_id) you could instead group the results using Ruby with group_by. This way you've each individual record for each group.

- task_groups = Task.all.group_by { |task| [task.event_id, task.person_id] }
- task_groups.each do |(event_id, person_id), tasks|
  = event_id
  = person_id
  = tasks.pluck(:id).join(', ')
  = tasks.pluck(:name).join(', ')

edited Jan 17, 2020 at 20:23

answered Jan 17, 2020 at 20:15

3limin4t0r

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Comments

Ravi Teja Gadi · Accepted Answer · 2020-01-17 19:47:32Z

1

If you are using postgres, you can get the result using following query.

Task.all.group(:event_id, :person_id).select("event_id,person_id,array_agg(id) as tasks")

answered Jan 17, 2020 at 19:47

Ravi Teja Gadi

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2 Comments

Yshmarov Over a year ago

Yes, using postgres

Ravi Teja Gadi Over a year ago

Then you can achieve the result using this query.

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