Is there a more efficient way to build a sorted hash from a collection of Ruby objects?

Question

I'm building a sorted hash for use in a grouped select in a rails app. I am not using ActiveRecord. Is there a more efficient or cleaner way than this?

def for_select
  select_list = {}
  Department.all.each do |dept|
    select_list[dept.top_level_department_cn] ||= []
    select_list[dept.top_level_department_cn] << [dept.cn, dept.sorid]
  end
  select_list.each_value { |select_options| select_options.sort_by!(&:first) }
             .sort
             .to_h
end

What's `Department.all` if it's not ActiveRecord? – Mark Thomas Aug 03 '17 at 11:44 — Mark Thomas, Aug 03 '17 at 11:44
It is a custom object for LDAP entries. – HarlemSquirrel Aug 03 '17 at 16:42 — HarlemSquirrel, Aug 03 '17 at 16:42

score 1 · Answer 1 · answered Aug 03 '17 at 00:55

1

def for_select
  Department.all
  .sort
  .group_by(&:top_level_department_cn)
  .each_value{|v| v.map!{|dept| [dept.cn, dept.sorid]}.sort_by!(&:first)}
end

answered Aug 03 '17 at 00:55

sawa

165,429
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Sort by itself doesn't work because `Department` is not an ActiveRecord model. I did forget about the `#group_by` enumerator which is very helpful here! – HarlemSquirrel Aug 03 '17 at 14:01
Also, sorting the initial set of departments with `sort_by(&:cn)` makes the second `#sort_by!` unnecessary. – HarlemSquirrel Aug 03 '17 at 14:03
1

If you define `<=>` on `Department` then `.sort` works. :) – Mark Thomas Aug 03 '17 at 16:45

score 1 · Answer 2 · answered Aug 03 '17 at 10:47

1

Another solution:

def for_select
  # @see: https://stackoverflow.com/questions/2698460#answer-28916684
  select_list = Hash.new { |h, k| h[k] = [] }

  Department.all
    .map { |d| [d.top_level_department_cn, [d.cn, d.sorid]] }
    .sort
    .each { |top_level_cn, data| select_list[top_level_cn] << data }

  select_list
end

answered Aug 03 '17 at 10:47

romainsalles

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I didn't know I could create a hash with default values. That is very cool! However, in the linked SO answer, the author recommends `Hash.new([].freeze)` and I do like that better. – HarlemSquirrel Aug 03 '17 at 14:02
That's right, but in this case you'll have to instantiate a new array each time: `.each { |top_level_cn, data| select_list[top_level_cn] += [data] }`, which is less intuitive in my point of view (you have to read this like this: `.each { |top_level_cn, data| select_list[top_level_cn] = select_list[top_level_cn] + [data] }`) – romainsalles Aug 03 '17 at 14:16

Is there a more efficient way to build a sorted hash from a collection of Ruby objects?

2 Answers2