Trying to deleting from Active Record collection ONLY using delete_if

Question

I want to remove elements from an Active Record collection, for this I'm trying to use delete_if. Below is my collection:

categories = Category.all
groups = Group.all

  result = []
  groups.each do |g|
    result.push({ :name => g[:name], :amount => g[amount_column], :drilldown => [] })
    categories.where( { :group_id => g.id } ).each do |c, index|
      result.last[:drilldown].push({ :name => c[:name], :amount => c[amount_column], :drilldown => nil })
    end
    # lastly, remove these categories from this collection (not working)
    categories.delete_if {|c| c.group_id == g.id }
    # tried this too - categories.select! { |c| c.group_id != g.id }
  end

  abort(categories.size.inspect)

..I want to do something with the categories of each group, then remove them form the array. After the loop block I'll want to be left with the categories which do not belong to a group - that is why I delete those of each group there. Here is the data for groups and categories when they are first fetched (sorry it's a lot but just to note that some category.group_id and group.id match:

#categories
#<ActiveRecord::Associations::CollectionProxy [#<Category id: 13, name: "Internet", user_id: 1, created_at: "2014-03-09 13:15:19", updated_at: "2014-03-15 05:13:47", amount: #<BigDecimal:7f0c283806e0,'0.0',9(18)>, group_id: nil, amount_in: #<BigDecimal:7f0c28380578,'0.0',9(18)>, amount_out: #<BigDecimal:7f0c283804b0,'0.0',9(18)>>, #<Category id: 15, name: "Electricity", user_id: 1, created_at: "2014-03-09 13:15:39", updated_at: "2014-03-15 05:14:03", amount: #<BigDecimal:7f0c2838f5a0,'0.0',9(18)>, group_id: nil, amount_in: #<BigDecimal:7f0c2838f460,'0.0',9(18)>, amount_out: #<BigDecimal:7f0c2838f2f8,'0.0',9(18)>>, #<Category id: 6, name: "Phone", user_id: 1, created_at: "2014-02-18 10:07:47", updated_at: "2014-03-15 05:16:21", amount: #<BigDecimal:7f0c2838e470,'0.0',9(18)>, group_id: nil, amount_in: #<BigDecimal:7f0c2838e308,'0.0',9(18)>, amount_out: #<BigDecimal:7f0c2838e240,'0.0',9(18)>>, #<Category id: 9, name: "Trains", user_id: 1, created_at: "2014-02-22 03:08:08", updated_at: "2014-03-15 05:16:21", amount: #<BigDecimal:7f0c2838d340,'-0.5E3',9(18)>, group_id: nil, amount_in: #<BigDecimal:7f0c2838d138,'0.0',9(18)>, amount_out: #<BigDecimal:7f0c2838cf08,'-0.5E3',9(18)>>, #<Category id: 5, name: "Resaurants", user_id: 1, created_at: "2014-02-17 12:12:44", updated_at: "2014-03-15 05:16:21", amount: #<BigDecimal:7f0c2839be18,'-0.235E3',9(18)>, group_id: 16, amount_in: #<BigDecimal:7f0c2839bc38,'0.0',9(18)>, amount_out: #<BigDecimal:7f0c2839baa8,'-0.235E3',9(18)>>, #<Category id: 14, name: "Gas", user_id: 1, created_at: "2014-03-09 13:15:27", updated_at: "2014-03-15 05:16:21", amount: #<BigDecimal:7f0c2839a680,'0.0',9(18)>, group_id: 16, amount_in: #<BigDecimal:7f0c2839a3d8,'0.0',9(18)>, amount_out: #<BigDecimal:7f0c2839a1d0,'0.0',9(18)>>, #<Category id: 3, name: "Snowboarding", user_id: 1, created_at: "2014-02-11 09:43:52", updated_at: "2014-03-15 05:16:21", amount: #<BigDecimal:7f0c28398d30,'-0.1111E4',9(18)>, group_id: 16, amount_in: #<BigDecimal:7f0c28398b28,'0.0',9(18)>, amount_out: #<BigDecimal:7f0c28398a38,'-0.1111E4',9(18)>>]>

# groups
#<ActiveRecord::Associations::CollectionProxy [#<Group id: 16, name: "Testing", user_id: 1, amount: #<BigDecimal:31c0ce8,'-0.1346E4',9(18)>, created_at: "2014-03-09 13:48:50", updated_at: "2014-03-15 05:35:57", amount_in: #<BigDecimal:31d3118,'0.0',9(18)>, amount_out: #<BigDecimal:26b9728,'-0.1346E4',9(18)>>, #<Group id: 17, name: "test", user_id: 1, amount: #<BigDecimal:31d2a88,'0.0',9(18)>, created_at: "2014-03-15 05:38:36", updated_at: "2014-03-15 05:39:00", amount_in: #<BigDecimal:31d14f8,'0.0',9(18)>, amount_out: #<BigDecimal:2e4e650,'0.0',9(18)>>]>

.. but my delete_if does nothing (abort shows the same size with or without the delete_if). Please note that there are group.id = 16, and category.group_id = 16 so the delete_if should delete those ones - but it doesn't. Is there anything that I'm doing wrong?

Answer 1

Try this ,I think it will help

categories.delete_if {|x| x.group_id==16}