Access properties of objects into nested Array - Javascript

Question

I'd like please to retrieve all text (text 1,text 2....) from the following array :

[
    {
    "reviews": 
    [
      {
        "_id": "5e84239d6e24358b50f3fe4e",
        "text": "My text 1"
      },
      {
        "_id": "5e8423a46e24358b50f3fe4f",
        "text": "My text 2"
      }
    ]
  },
  {
    "reviews": 
    [
      {
        "_id": "5e84239d6e24358b50f3fe4e",
        "text": "My text 3"
      },
      {
        "_id": "5e8423a46e24358b50f3fe4f",
        "text": "My text 4"
      }
    ]
  },
  {
    "reviews": 
    [
      {
        "_id": "5e84239d6e24358b50f3fe4e",
        "text": "My text 5"
      },
      {
        "_id": "5e8423a46e24358b50f3fe4f",
        "text": "My text 6"
      }
    ]
  }
]

This array is stored in a variable called stores.

I have tried the following :

const listText = stores.map(count => count.reviews.text // [null, null, null]
const listText = stores.map((count, i) => count.reviews[i].text) // Cannot read property 'text' of undefined
const listText = stores.forEach((key, i) => key.reviews[i].text) // Cannot read property 'text' of undefined

Could you please help me out here, Many thanks

elvira.genkel · Accepted Answer · 2020-04-01 13:39:08Z

1

You can't use count.reviews.text as reviews is an array, so you should also iterate through reviews:

const data = [
{
"reviews": 
[
  {
    "_id": "5e84239d6e24358b50f3fe4e",
    "text": "My text 1"
  },
  {
    "_id": "5e8423a46e24358b50f3fe4f",
    "text": "My text 2"
  }
]
  },
  {
"reviews": 
[
  {
    "_id": "5e84239d6e24358b50f3fe4e",
    "text": "My text 3"
  },
  {
    "_id": "5e8423a46e24358b50f3fe4f",
    "text": "My text 4"
  }
]
  },
  {
"reviews": 
[
  {
    "_id": "5e84239d6e24358b50f3fe4e",
    "text": "My text 5"
  },
  {
    "_id": "5e8423a46e24358b50f3fe4f",
    "text": "My text 6"
  }
]
  }
]  

const listText = data.reduce((acc,current) => acc.concat(current.reviews.map(it => it.text)), [])

console.log(listText)

answered Apr 1, 2020 at 13:39

elvira.genkel

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3 Comments

Said951 Over a year ago

Yes, it works perfectly :) Thanks. And what about if I wanted to pick just some values from the array and not others ? In my example, I have just _id and text. But suppose I have also other properties such as photo, slug.... How can I make sure to pick just _id and text but NOT the other properties ?

elvira.genkel Over a year ago

Could you please clarify the desired output? if you have an array of objects with lots of fields and you need to convert it to list of objects with just 2 fields? e.g.

const initialArr = [{id:1, text:'abc', rank:5, etc:'some vale'}, {id:2, text:'rwr', rank:3, etc:'some vale'}, {id:3, text:'36y3563', rank:6, etc:'some vale'}]

you can use .map function: initialArray.map(item=> ({id: item.id, text:item.text}))

Said951 Over a year ago

This is exactly what I needed. You've been very helpful Elivra, many thanks !

mplungjan · Accepted Answer · 2020-04-01 14:16:57Z

1

Map and flat:

const data = [ 
{ "reviews": [ { "_id": "5e84239d6e24358b50f3fe4e", "text": "My text 1" }, { "_id": "5e8423a46e24358b50f3fe4f", "text": "My text 2" } ] }, 
{ "reviews": [ { "_id": "5e84239d6e24358b50f3fe4e", "text": "My text 3" }, { "_id": "5e8423a46e24358b50f3fe4f", "text": "My text 4" } ] }, 
{ "reviews": [ { "_id": "5e84239d6e24358b50f3fe4e", "text": "My text 5" }, { "_id": "5e8423a46e24358b50f3fe4f", "text": "My text 6" } ] } ] 
console.log(
  data.map(items => items.reviews.map(review => review.text)).flat()
)

answered Apr 1, 2020 at 14:16

mplungjan

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1 Comment

Said951 Over a year ago

Without using .flat() it works, even though I get arrays into array. But when using .flat(), I log flat is not a function. Thanks @mplungjan

Abhishek Kulkarni · Accepted Answer · 2020-04-01 13:39:35Z

0

Try this below :

let output = [];
            input.map(function (item_1) {
                item_1.reviews.map(function (item_2) {
                  output.push(item_2.text);
                })
            });

answered Apr 1, 2020 at 13:39

Abhishek Kulkarni

1,7671 gold badge8 silver badges9 bronze badges

1 Comment

Said951 Over a year ago

Thanks @Abhishek Kulkarni :)

Nick Parsons · Accepted Answer · 2020-04-01 13:42:53Z

Using .flatMap(), you can iterate over each object and then .map() the reviews array of each object to an array of containing the text properties. .flatMap() allows you to flatten all the inner map array results into the one larger resulting array.

const stores = [ { "reviews": [ { "_id": "5e84239d6e24358b50f3fe4e", "text": "My text 1" }, { "_id": "5e8423a46e24358b50f3fe4f", "text": "My text 2" } ] }, { "reviews": [ { "_id": "5e84239d6e24358b50f3fe4e", "text": "My text 3" }, { "_id": "5e8423a46e24358b50f3fe4f", "text": "My text 4" } ] }, { "reviews": [ { "_id": "5e84239d6e24358b50f3fe4e", "text": "My text 5" }, { "_id": "5e8423a46e24358b50f3fe4f", "text": "My text 6" } ] } ];

const res = stores.flatMap((o) => o.reviews.map(({text}) => text));
console.log(res);

If you can't support .flatMap(), you can always map to an array of arrays, using .map() and then flatten it after using .concat() with the spread syntax (...):

const stores = [ { "reviews": [ { "_id": "5e84239d6e24358b50f3fe4e", "text": "My text 1" }, { "_id": "5e8423a46e24358b50f3fe4f", "text": "My text 2" } ] }, { "reviews": [ { "_id": "5e84239d6e24358b50f3fe4e", "text": "My text 3" }, { "_id": "5e8423a46e24358b50f3fe4f", "text": "My text 4" } ] }, { "reviews": [ { "_id": "5e84239d6e24358b50f3fe4e", "text": "My text 5" }, { "_id": "5e8423a46e24358b50f3fe4f", "text": "My text 6" } ] } ];

const res = [].concat(...stores.map((o) => o.reviews.map(({text}) => text)));
console.log(res);

Perfect, it works perfectly @Nick Parsons. You've made my day :) Great explanation

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