Create a nested hash - arrays

Question

I have an array like this:
[
{:game_id=>546012, :period=>:fg, :stat_name=>:hits, :result=>12, :team_id=>1104},
{:game_id=>546012, :period=>:fg, :stat_name=>:errors, :result=>1, :team_id=>1104},
{:game_id=>546012, :period=>:fg, :stat_name=>:hits, :result=>9, :team_id=>1103},
{:game_id=>546012, :period=>:fg, :stat_name=>:errors, :result=>3, :team_id=>1103}
]
How can turn it into an array of items like this:
{ 546012 => { :hits => { :fg => { 1104 => 12,
1103 => 9 } }
:errors => { :fg => { 1104 => 1,
1103 => 3 } } }

Answer 1

First, create a hash organized by :game_id
{ 546012 => {{
{:period=>:fg, :stat_name=>:hits, :result=>12, :team_id=>1104},
{:period=>:fg, :stat_name=>:errors, :result=>1, :team_id=>1104},
{:period=>:fg, :stat_name=>:hits, :result=>9, :team_id=>1103},
{:period=>:fg, :stat_name=>:errors, :result=>3, :team_id=>1103}
]}
Then group by :stat_name
{ 546012 => [
{:hits => [
{:period=>:fg, :result=>12, :team_id=>1104},
{:period=>:fg, :result=>9, :team_id=>1103}],
:errors => [
{:period=>:fg, :result=>1, :team_id=>1104},
{:period=>:fg, :result=>3, :team_id=>1103}
]}
]}
Then group by period:
{ 546012 => [
{:hits => [
:fg => [{:result=>12, :team_id=>1104},
{:result=>9, :team_id=>1103}]
]}
]},
:errors => [
:fg => [{:result=>1, :team_id=>1104},
{:result=>3, :team_id=>1103}]
]}
]}
Lastly, group by :team_id and associate each one to its :result.
{ 546012 => [
{:hits => [
:fg => [1104 => 12, 1103 => 9]
]},
:errors => [
:fg => [1104 => 1, 1103 => 3]
]}
]}
As for how to create these groupings, I will leave it as an exercise to you.
One possible method is to loop through each item and create a new copy of the object that stores these new mappings. For instance, if we have this object:
foods = {
{:food => lemon, :taste => sour},
{:food => pretzel, :taste => salty},
{:food => pretzel, :taste => sweet}
}
We could group by foods like (pseudocode):
newfoods = {};
foreach item in foods:
newfoods[ item.food ].push( item.taste );
And end up with
newfoods = [
{ lemon => [sour] },
{ pretzel => [sweet, salty] }
]

Answer 2

The best option you can do is flatten it.
Credits go to this question.