防止转换后的数组中出现 Nil 值

Question

删除nils是quite simple，但是，我想知道：

1) 我做错了什么，为什么我下面的数组结果包含 nils?

2) 如何防止 nils 添加到我的数组中，而不是事后删除它们。

@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.

我也尝试过@theTinMan 的 recommendation 先 select，然后 map，但我得到了相同的结果：

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]]}]

我曾尝试使用哈希代替 @cars 的数组，但取得了部分成功。这防止了 nils，但我的最终目标是在下面构建 "drilldown: series[]"，这是一个哈希数组：

// 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

我会选择更多的 reduce 方法，因为您正在获取一个列表并将其归结为另一个对象。 each_with_object 执行 reduce 但隐含地 returns 每个循环中的 obj（在本例中为汽车）

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

旁注：地图通常更多地用于转换或等效更改，这就是我认为这里感觉不对的原因。

Answer 2

我建议按 id 分组，然后创建 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]}]}
#  }

编辑 - 更新确实匹配原始问题的编辑（获取 Highcharts 的系列数据）

这应该return要求的结果：

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]]}]

第一部分构建这样的哈希。

#=> {"Chevy"=>[["Camaro", 20]], "Ford"=>[["Mustang", 55], ["Fusion", 150]]}

将 Hash.new([]) 作为对象传递允许将元素插入默认数组。

最终哈希映射到所需的键。

Answer 3

您的代码之所以如此，是因为 array[8] = x 在数组的第 8 位插入 x，而 ruby 用 nils 填充最多 8 个空格。

a = []
a[7] = 4
a == [nil, nil, nil, nil, nil, nil, nil, 4]

您需要 @cars 才能成为哈希 - 而不是数组

我认为这会完成您想要做的事情：

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

这实际上与@Austio 的解决方案几乎相同。

防止转换后的数组中出现 Nil 值

Prevent Nil Values in Transformed Array

ruby

arrays

json

highcharts

ruby-on-rails-4