Prevent Nil Values in Transformed Array - arrays

Question

Removing nils is quite simple, however, I'd like to know:
1) What am I doing wrong, why does my array result below include nils?
2) How I can PREVENT the nils from being added to my array, instead of removing them after the fact.
#cars = Array.new
plucked_array = [
[8, "Chevy", "Camaro", 20],
[9, "Ford", "Mustang", 55],
[9, "Ford", "Fusion", 150]
]
plucked_array.
each { |id, make, model, model_count|
#cars[id] ||= {name: make, id: make, data: []}
#cars[id][:data].push([model, model_count])
}
puts #cars.inspect
#=>[nil, nil, nil, nil, nil, nil, nil, nil, {:name=>"Chevy", :id=>"Chevy", :data=>[["Camaro", 20]]}, {:name=>"Ford", :id=>"Ford", :data=>[["Mustang", 55], ["Fusion", 150]]}]
puts #cars.compact.inspect
#=>[{:name=>"Chevy", :id=>"Chevy", :data=>[["Camaro", 20]]}, {:name=>"Ford", :id=>"Ford", :data=>[["Mustang", 55], ["Fusion", 150]]}]
# This gives the result I'm looking for,
# just wondering how to best get transformed array without the post-cleanup.
I also attempted #theTinMan's recommendation to select first, then map, but I had the same results:
plucked_array.select { |id, make, model, model_count|
#cars[id] = {'name' => make, 'id' => make, 'data' => []}
}.map { |id, make, model, model_count|
#cars[id]['data'].push([model, model_count])
}
puts #cars.inspect
#=>[nil, nil, nil, nil, nil, nil, nil, nil, {:name=>"Chevy", :id=>"Chevy", :data=>[["Camaro", 20]]}, {:name=>"Ford", :id=>"Ford", :data=>[["Mustang", 55], ["Fusion", 150]]}]
I've tried, with partial success, to use Hash instead of an array for #cars. This prevented nils, but my end goal is to build "drilldown: series[]" below, which is an array of hashes:
// Create the chart
Highcharts.chart('container', {
chart: {
type: 'column'
},
title: {
text: 'Imaginary Car Stats'
},
subtitle: {
text: 'Click the columns to view models.'
},
xAxis: {
type: 'category'
},
yAxis: {
title: {
text: 'Total car count'
}
},
legend: {
enabled: false
},
plotOptions: {
series: {
borderWidth: 0,
dataLabels: {
enabled: true,
format: '{point.y}'
}
}
},
tooltip: {
headerFormat: '<span style="font-size:11px">{series.name}</span><br>',
pointFormat: '<span style="color:{point.color}">{point.name}</span>: <b>{point.y:.2f}%</b> of total<br/>'
},
/*I have separate `pluck` query for this top-level series:*/
"series": [
{
"name": "Cars",
"colorByPoint": true,
"data": [
{
"name": "Ford",
"y": 205,
"drilldown": "Ford"
},
{
"name": "Chevy",
"y": 20,
"drilldown": "Chevy"
},
{
"name": "Other",
"y": 16,
"drilldown": null
}
]
}
],
"drilldown": {
/*This is the array of hashes I'm attempting to create:*/
"series": [
{
"name": "Ford",
"id": "Ford",
"data": [
[
"Fusion",
150
],
[
"Mustang",
55
]
]
},
{
"name": "Chevy",
"id": "Chevy",
"data": [
[
"Camaro",
20
]
]
}
]
}
});
<script src="https://code.highcharts.com/highcharts.js"></script>
<script src="https://code.highcharts.com/modules/data.js"></script>
<script src="https://code.highcharts.com/modules/drilldown.js"></script>
<div id="container" style="min-width: 310px; height: 400px; margin: 0 auto"></div>

Answer 1

The reason your code is behaving the way it does is because array[8] = x inserts x at position 8 in the array, and ruby fills the spaces up to 8 with nils.
a = []
a[7] = 4
a == [nil, nil, nil, nil, nil, nil, nil, 4]
You need #cars to be a hash - not an array
I think this will do what you are trying to do:
plucked_array = [
[8, "Chevy", "Camaro", 20],
[9, "Ford", "Mustang", 55],
[9, "Ford", "Fusion", 150]
]
cars = plucked_array.each_with_object({}) do |(id, make, model, count), cars|
cars[id] ||= {id: id, make: make, data: []}
cars[id][:data] << [model, count]
end
p cars.values
Which actually is almost identical to #Austio's solution.

Answer 2

I would go for more of a reduce approach because you are taking a list and boiling it down into another object. each_with_object does the reduce but implicitly returns the obj (in this case cars) in every loop
new_list = plucked_array.each_with_object({}) do |(id, make, model, model_count), cars|
# return before mutating cars hash if the car info is invalid
cars[id] ||= {name: make, id: make, data: []}
cars[id][:data].push([model, model_count])
end
# Then in your controller to handle the usage as an array
#cars = new_list.values
Side note: map is normally more for transforms or equivalent changes, which is i think why it feels off here.

Answer 3

I suggest grouping by id, then creating a hash:
plucked_array.group_by(&:first).transform_values{ |v| v.map{ |id, make, model, model_count| {name: make, id: make, data: [model, model_count]} }}
# {8=>[{:name=>"Chevy", :id=>"Chevy", :data=>["Camaro ls", 20]}],
# 9=>[{:name=>"Ford", :id=>"Ford", :data=>["Mustang", 55]}, {:name=>"Ford", :id=>"Ford", :data=>["Fusion", 150]}]}
# }
Edit - update do match the edit of the original question (get series of data for Highcharts)
This should return the required result:
plucked_array.map.with_object(Hash.new([])) { |(id, make, model, model_count), h|
h[make] += [[model, model_count]] }.map { |k, v| {name: k, id: k, data: v }}
#=> [{:name=>"Chevy", :id=>"Chevy", :data=>[["Camaro", 20]]}, {:name=>"Ford", :id=>"Ford", :data=>[["Mustang", 55], ["Fusion", 150]]}]
The first part builds an hash like this.
#=> {"Chevy"=>[["Camaro", 20]], "Ford"=>[["Mustang", 55], ["Fusion", 150]]}
Passing Hash.new([]) as object allows to insert elements to the default array.
Finally the hash is mapped to the required keys.