Retrieve the two latest items in a dictionary array based on their order date

Question

Retrieve the two latest items in a dictionary array based on their order date

I've been browsing through similar discussions, but I just can't seem to grasp the concept. The JSON data for my current item appears to be more complicated than I anticipated. Here is a snippet of the lengthy JSON data:

items = [
      {
        'name' : 'Books',
        'types':[
          {
              'name' : 'Hard Cover',
              'genres':[
                {
                  'genre' : 'Romance',

                  'added_date' : '2018-09-15',

                  'id':1
                },
                {
                  'genre' : 'Crime',

                  'added_date' : '2018-10-01',

                  'id' : 2
                }

              ],
              'cover':['pic1.png','pic2.png']
              },
              {
                'name' : 'Audio',
                'genres':[
                  {
                    'genre' : 'Memoir',

                    'added_date' : '2018-08-01',

                    'id' : 3
                  }

                ],
                'pictures':['pic3.png','pic4.png']
           },

         ]

      },

      {
        'name' : 'Videos',
        'types':[
          {
              'name' : 'English',
              'genres':[
                {
                  'genre' : 'Comedy',

                  'added_date' : '2018-10-14',

                  'id' : 12
                }

              ],
              'pictures':['pic5.png','pic6.png']
              }

         ]

      }
  ];

What I'm aiming for now is to extract the 3 most recently added items based on their "added_date" within the "genres" block. For these items, I would like to generate an array with dictionary elements containing the full path information:

   [
    {'id':7,'genre':'Romance','name':'Hard Cover','added_date':'2018-09-16','top_parent_name':'Books'},
    {'id':8,'genre':'Memoir','name':'Audio','added_date':'2018-09-15','top_parent_name':'Books'},


     ]

The goal is to identify and retrieve the latest 3 items added throughout the entire dataset based on their "added_date" field, along with relevant details. I hope this clarifies the objective.

So far, I have brainstormed some ideas, but implementing them has proven to be quite complex.

items.forEach(function(value, index, array) {
      const types: any[] = value['types'];

      types.forEach(function(value_t, index_t, array_t){
        const genres: any[] = value_model['genes'];
       //loop again to get date....

      });



  });

javascript typescript

Answer 1

Answer №1

One method to consider is extracting the desired data into objects through multiple levels of mapping followed by flattening. Using Array.prototype.flatten may not be universally supported yet, so for now, reduce(concat) can be utilized.

Once the data is transformed into a flat list, sort it in descending order based on the date. Finally, retrieve the top three values:

const items = [{"name": "Books", "types": [{"cover": ["pic1.png", "pic2.png"], "genres": [{"added_date": "2018-09-15", "genre": "Romance", "id": 1}, {"added_date": "2018-10-01", "genre": "Crime", "id": 2}], "name": "Hard Cover"}, {"genres": [{"added_date": "2018-08-01", "genre": "Memoir", "id": 3}], "name": "Audio", "pictures": ["pic3.png", "pic4.png"]}]}, {"name": "Videos", "types": [{"genres": [{"added_date": "2018-10-14", "genre": "Comedy", "id": 12}], "name": "English", "pictures": ["pic5.png", "pic6.png"]}]}];

const tops = items.map(item => item.types.map(type => type.genres.map(genre => ({
  name: type.name,
  top_name: item.name,
  ...genre
})))).reduce(
  (a, b) => a.concat(b), []
).reduce(
  (a, b) => a.concat(b), []
).sort(
  (a, b) => a.added_date > b.added_date ? -1 : a.added_date < b.added_date ? 1 : 0
).slice(0, 3)

console.log(tops)

There may be some inefficiencies with these individual loops, and the sorting process might have a time complexity of O(n * log(n)), whereas a simple maximum of three parts should ideally be O(n). However, addressing these concerns becomes necessary only if they pose a bottleneck in your application.

Answer 2

One method to consider is extracting the desired data into objects through multiple levels of mapping followed by flattening. Using Array.prototype.flatten may not be universally supported yet, so for now, reduce(concat) can be utilized.

Once the data is transformed into a flat list, sort it in descending order based on the date. Finally, retrieve the top three values:

const items = [{"name": "Books", "types": [{"cover": ["pic1.png", "pic2.png"], "genres": [{"added_date": "2018-09-15", "genre": "Romance", "id": 1}, {"added_date": "2018-10-01", "genre": "Crime", "id": 2}], "name": "Hard Cover"}, {"genres": [{"added_date": "2018-08-01", "genre": "Memoir", "id": 3}], "name": "Audio", "pictures": ["pic3.png", "pic4.png"]}]}, {"name": "Videos", "types": [{"genres": [{"added_date": "2018-10-14", "genre": "Comedy", "id": 12}], "name": "English", "pictures": ["pic5.png", "pic6.png"]}]}];

const tops = items.map(item => item.types.map(type => type.genres.map(genre => ({
  name: type.name,
  top_name: item.name,
  ...genre
})))).reduce(
  (a, b) => a.concat(b), []
).reduce(
  (a, b) => a.concat(b), []
).sort(
  (a, b) => a.added_date > b.added_date ? -1 : a.added_date < b.added_date ? 1 : 0
).slice(0, 3)

console.log(tops)

There may be some inefficiencies with these individual loops, and the sorting process might have a time complexity of O(n * log(n)), whereas a simple maximum of three parts should ideally be O(n). However, addressing these concerns becomes necessary only if they pose a bottleneck in your application.

Answer 3

Answer №2

If I understand your question correctly, you are looking to extract the most recent 3 items based on their date of addition and convert them into a specific format. The solution will vary based on the amount of data being processed. One approach is to create a completely flat array of the data and then sort it by date. To achieve this, you can use an array flattening utility function (I have provided one below, but using lodash is recommended if possible).

Here's an example:

const flatten = arr => arr.reduce((a, b) => a.concat(b), [])

const mapGenres = (topName, name, genres) => genres.map(genre => ({
  name,
  topName,
  ...genre
})

const result = flatten(items.map(({ name, types }) => 
  flatten(types.map(type => mapGenres(name, type.name, type.genres)))
))

result.sort((a, b) => return b.added_date.localeCompare(a.added_date))

This code is untested, but it should be relatively simple to follow. By nesting levels of flattening and mapping functions, you can achieve the desired output structure.

Answer 4

If I understand your question correctly, you are looking to extract the most recent 3 items based on their date of addition and convert them into a specific format. The solution will vary based on the amount of data being processed. One approach is to create a completely flat array of the data and then sort it by date. To achieve this, you can use an array flattening utility function (I have provided one below, but using lodash is recommended if possible).

Here's an example:

const flatten = arr => arr.reduce((a, b) => a.concat(b), [])

const mapGenres = (topName, name, genres) => genres.map(genre => ({
  name,
  topName,
  ...genre
})

const result = flatten(items.map(({ name, types }) => 
  flatten(types.map(type => mapGenres(name, type.name, type.genres)))
))

result.sort((a, b) => return b.added_date.localeCompare(a.added_date))

This code is untested, but it should be relatively simple to follow. By nesting levels of flattening and mapping functions, you can achieve the desired output structure.

Retrieve the two latest items in a dictionary array based on their order date

Answer №1

Answer №2

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