How to make a "pivot table" on Ruby on Rails? - ruby-on-rails

Question

First, I'd like to mention I'm COMPLETELY new to Ruby and Rails, I'm on my very first days of learning, so I apologize if I seem a bit unclear or too broad with my questions.
I'm trying to do something simple (I think?), which is to pivot a table.
I have a table that looks like this:
----------------------------------
| Name | Product ID | Amount |
|----------|----------------------
| Robert | P1 | 2 |
| Michael | P2 | 1 |
| Leonard | P2 | 1 |
| Robert | P2 | 4 |
| Robert | P3 | 2 |
| Michael | P3 | 1 |
----------------------------------
... and I'd like to to turn it into something like this:
---------------------------
| Name | P1 | P2 | P3 |
---------------------------
| Robert | 2 | 4 | 2 |
| Michael | - | 1 | 1 |
| Leonard | - | 1 | - |
---------------------------
I'm not too sure how to achieve that. I've looked around and haven't found anything specific to my question.
I found a gem called pivot_table, which can be found here: https://github.com/edjames/pivot_table but I have no clue how to exactly use it. It has a small guide in it, but I don't know where to place the code.
Any help is greatly appreciated.
Thank you.

Answer 1

Looking at your table and the results you're looking for, I would do it like this ( I assume it's an orders table ?)
result = []
Order.all.group_by(&:name).each do |name, orders|
record = {}
record["name"] = name
orders.each do |order|
record[order.product_id] = order.amount
end
result.append(record)
end
I hope this will give you a good starting point !

Answer 2

First install the gem
# In your Gemfile
gem 'pivot_table'
Then in your terminal, run
bundle install
Say the model represented by your first table is Sale.
sales = Sale.all
grid = PivotTable::Grid.new do |g|
g.source_data = sales
g.column_name = :product_id
g.row_name = :name
end
Then you can use the other methods listed in the docs. For example
g.column_headers # ['P1', 'P2', 'P3']
Note: this is just from reading the GitHub page you linked. I've never used the gem.
Edit:
You can put the code in a module:
# lib/PivotTable
module PivotTable
def grid(data, options = {})
grid = PivotTable::Grid.new do |g|
g.source_data = data
g.column_name = options[:column_name]
g.row_name = options[:row_name]
end
end
end
Then you'd call it from somewhere else with
include PivotTable
def my_method
sales = Sale.all
grid = grid(sales, { :row_name => :name, :column_name => :product_id })
# do stuff
end
This way you can reuse the grid-generating code and call it with arbitrary parameters.

Answer 3

This is a general solution, that I implemented in application_helper.rb
def pivot_table row_model, column_model, pivot_model, pivot_attribute
row_model.all.map do |r|
column_model.select(:id).sort.map do |c|
pivot_model.find_by(
row_model.to_s.downcase => r,
column_model.to_s.downcase => c
)&.public_send(pivot_attribute) || 0
end
end
end
The first three parameters are capital-letter ActiveRecord subclass names, and the pivot_attribute (which is an attribute of pivot_model) can be given as a symbol or a string. This assumes pivot_model is a many-to-many relation that references row_model and column_model as foreign keys. If there isn't a many-many model, I'm guessing some models could be repeated among the parameters, but I haven't kitchen tested it for that.
The return value is an array of arrays.