Building array of data in Ruby

Question

I have the results of a search in an instance var called @results. Each item is an album. I have looped over the result set and added all the album parent collection id's to a var called @collections. This is done as below:

 @results.each do |album|
  @collections << album.collection_id
end

@collections = @collections.uniq

I now need to re iterate over the @results and create a child array of each album id that belongs in each collection.

I will then be able to use this to build nice output in my view.

I am rather confused as to how to build that child array of album id's per collection id.

Any help on this?

Arup Rakshit · Accepted Answer · 2014-04-10 20:53:41Z

2

I now need to re iterate over the @results and create a child array of each album id that belongs in each collection.

You need to use group_by method :

child_array_by_id = @results.group_by { |album| album.collection_id }
@collections = child_array_by_id.keys
# now iterate
child_array_by_id.each do |id_key, val|
   # your code
end

Now you don't need the below to get the @collection array also. Because child_array_by_id.keys is giving you the same.

@results.each do |album|
  @collections << album.collection_id
end

@collections = @collections.uniq

edited Apr 10, 2014 at 20:53

answered Apr 10, 2014 at 20:48

Arup Rakshit

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1 Comment

rctneil Over a year ago

That's brilliant. Still trying to wrap my head around how it works but thanks!

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