Merge a single array into nested array in rails

Question

I have a list of objects something like this:

      a = [
          {
              id: 0,
              name: "ABC",
              work: "ABC2"
          },
          {
              id: 0,
              name: "XYZ",
              work: "XYZ2"
          },
          {
              id: 1,
              name: "ACD",
              work: "ACD2"
          }
      ]

And I want to convert it into something like this:

      b = [
            {
              id: 0,
              fields: [
                  {
                    name: "ABC",
                    work: "ABC2"
                  },
                  {
                    name: "XYZ",
                    work: "XYZ2"
                  }
                ]
            },

            {
                id: 1,
                fields: [
                    {
                        name: "ACD",
                        work: "ACD2"
                    }
                ]
            }
      ]

The idea is to group the objects (by id) in one array.

The approach I tried is:

      b = []

      rest_object = []

      a.each_with_index do |aa, idx|

        aa.delete(:id)

        rest_object << aa

        if idx == 0
          next
        end

        puts a[idx][:id], a[idx-1][:id]

        if a[idx][:id] != a[idx-1][:id]
          b << {id: a[idx-1][:id], names: rest_object}
          rest_object = []
        end

      end

But I am getting an empty output.

Also, if it is possible to achieve the same in some cleaner way. That would be helpful.

3limin4t0r · Accepted Answer · 2019-10-10 15:12:11Z

1

Something like this does the job. This deletes the :id key-value pair from each hash and uses the value to group the remainder of the hash. Then map the resulting hash to created an array and transform the data into {id: ..., fields: ...} format.

a = [{id: 0, name: "ABC", work: "ABC2"}, {id: 0, name: "XYZ", work: "XYZ2"}, {id: 1, name: "ACD", work: "ACD2"}]

b = a.group_by { |hash| hash.delete(:id) }
     .map { |id, fields| {id: id, fields: fields} }
#=> [{:id=>0, :fields=>[{:name=>"ABC", :work=>"ABC2"}, {:name=>"XYZ", :work=>"XYZ2"}]}, {:id=>1, :fields=>[{:name=>"ACD", :work=>"ACD2"}]}]

Note: This mutates the hashes in the a array. If you don't want this change a.group_by to a.map(&:dup).group_by. Which first duplicates all hashes before doing any mutations.

edited Oct 10, 2019 at 15:12

answered Oct 10, 2019 at 11:43

3limin4t0r

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1 Comment

3limin4t0r Over a year ago

To run this in irb surround the whole thing with a begin/end block, or move the dot before map to the end of the group_by line.

ray · Accepted Answer · 2019-10-10 10:16:44Z

0

Try following,

required_keys = a[0].except(:id).keys
b = a.group_by { |x| x[:id] }

b = b.inject([]) do |m,(k,v)|
      arr =  { id: k }
      required_keys.each do |key|
        arr[key.to_s.pluralize.to_sym] = v.map { |z| z.slice(key) }
      end
      m << arr
    end

# => [{:id=>0, :names=>[{:name=>"ABC"}, {:name=>"XYZ"}]}, {:id=>1, :names=>[{:name=>"ACD"}]}]

edited Oct 10, 2019 at 10:16

answered Oct 10, 2019 at 9:46

ray

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5 Comments

Bhawan Over a year ago

Right now, it is taking only names field in slice. I want every field other than id. There are around 30-40 fields.

Bhawan Over a year ago

Sorry if I was not clear, but I meant this. :names=>[{:name=>"ABC", :work=>"ABC"}, {:name=>"XYZ", :work=>"XYZ"}]

ray Over a year ago

can you provide elaborated input and output example? @Bhawan

rahul mishra Over a year ago

Use this if you want all data inside names a.group_by { |x| x[:id] }.inject([]) { |m,(k,v)| m << { id: k, names: v.map { |z| z.slice(*(z.keys-[:id])) } } }

ray Over a year ago

@rahulmishra Great, It is real headache when question is not clear with appropriate example :P

Ashok Damaniya · Accepted Answer · 2019-10-10 10:26:51Z

0

  a = [
      {
          id: 0,
          name: "ABC"
      },
      {
          id: 0,
          name: "XYZ"
      },
      {
          id: 1,
          name: "ACD"
      }
  ]

ary = []
a.each do|val|
 ary[val[:id]] = {id: val[:id]} unless ary[val[:id]] 
 ary[val[:id]][:names] = [] unless ary[val[:id]][:names]
 ary[val[:id]][:names].push({name: val[:name]})
end

answered Oct 10, 2019 at 10:26

Ashok Damaniya

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Comments

iGian · Accepted Answer · 2019-10-10 10:29:04Z

If I understand, given a more general array like this:

a = [ { id: 0, name: "ABC", etc: "01" },
      { id: 0, name: "XYZ", etc: "02" },
      { id: 1, name: "ACD", etc: "11" } ]

The first idea I came up with is doing something like this:

require 'active_support/inflector' # for using pluralize

res = a.group_by{ |h| h[:id] }.values.map do |ary|
        h = Hash.new{ |h,k| h[k] = [] }
        ary.each { |hh| hh.each { |k,v| h[k] << v } }
        h[:id] = h[:id].first
        h.transform_keys do |k|
          unless k == :id
            k.to_s.pluralize.to_sym
          else
            k
          end
        end
      end

res #=> [{:id=>0, :names=>["ABC", "XYZ"], :etcs=>["01", "02"]}, {:id=>1, :names=>["ACD"], :etcs=>["11"]}]

This is not exactly the format you require, but to get that format, just change this line

ary.each { |hh| hh.each { |k,v| h[k] << v } }

to

ary.each { |hh| hh.each { |k,v| h[k] << { k => v } } }

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