Sort an array of objects in ruby - ruby

Question

First of all full disclosure. I attempted to solve this issue at this thread but I wanted to repost in hopes of getting some help in Ruby:
best way to sort an array of objects by category and infinite subcategory
I have made a feeble attempt a that solution but can't even get close and it's not even worth showing. Below is my attempt. It would mean the world to me if someone could give some good direction on this.
data = [{id: 1, name: "parent test 1", parent_id: nil, top_level_category_id: nil},
{id: 2, name: "test 2", parent_id: 1, top_level_category_id: 1},
{id: 3, name: "test 3", parent_id: 1, top_level_category_id: 1},
{id: 4, name: "parent test 4", parent_id: nil, top_level_category_id: nil},
{id: 5, name: "test 5", parent_id: 3, top_level_category_id: 4},
{id: 6, name: "test 6", parent_id: 4, top_level_category_id: 4},
{id: 7, name: "test 7", parent_id: 4, top_level_category_id: 4}]
This is what I am hoping to accomplish
parent test 1
test 2
test 3
test 5
parent test 2
test 6
test 7
-
ord_cat = {}
for item in data
if item[:parent_id] == nil
ord_cat[item[:id]] = {:name => item[:name], :children => {}}
end
end
# fill child directories
for item in data
if item[:parent_id] != nil
ord_cat[item[:top_level_category_id]][:children].merge!({item[:id] => item[:name]})
end
end
puts ord_cat
This is the output
{1=>{:name=>"parent test 1", :children=>{2=>"test 2", 3=>"test 3", 5=>"test 5"}}, 4=>{:name=>"parent test 4", :children=>{6=>"test 6", 7=>"test 7"}}}
This is clearly not nesting "test 5" properly. I'm not thrilled with the structure of the object.

Answer 1

We can construct the ancestor list for each node and sorting based on that list, in effect giving a depth-first traversal of the tree.
A bit lengthy solution, but would solve the problem I believe. Have used hash more to avoid scanning the array multiple times.
data = [{id: 1, name: "parent test 1", parent_id: nil, top_level_category_id: nil},
{id: 2, name: "test 2", parent_id: 1, top_level_category_id: 1},
{id: 3, name: "test 3", parent_id: 1, top_level_category_id: 1},
{id: 4, name: "parent test 4", parent_id: nil, top_level_category_id: nil},
{id: 5, name: "test 5", parent_id: 3, top_level_category_id: 4},
{id: 6, name: "test 6", parent_id: 4, top_level_category_id: 4},
{id: 7, name: "test 7", parent_id: 4, top_level_category_id: 4}]
# Amount of indentation for printing each node's nesting
INDENTATION_PER_LEVEL = 1
id_to_data_map = {}
id_to_parent_id_map = {}
data.each { |d|
id_to_data_map[d[:id]] = d
id_to_parent_id_map[d[:id]] = d[:parent_id]
}
data_with_ancestors = {}
data.each do |record|
ancestors = [record[:name]]
# Temporary parent
parent = record
while true do
parent_id = id_to_parent_id_map[parent[:id]]
break if parent_id.nil? # Hit the root - get out.
parent = id_to_data_map[parent_id]
ancestors << parent[:name]
end
# Construct a list of ancestors for the node, with the oldest ancestor first.
data_with_ancestors[record[:name]] = ancestors.reverse
end
# Sort the flattened list based on the ancestor string constructed by joining all the parent names.
sorted_list = data_with_ancestors.sort_by {|name, ancestors| ancestors.join(" ")}
# Add indentation for the record names based on their nesting in the tree.
print_info = sorted_list.collect {|name, ancestors| (" " * (ancestors.size - 1) * INDENTATION_PER_LEVEL) + name}
print_info.each { |record| puts record }