read array in javascript

Question

I am new in javascript and using nodejs and mongoose query to get a result which I would like to loop through and get some values in another array.

The resultset looks like

[ { _id: 5366e9049cfc825b32966852,
 companies:
     [ 5ab20bb69cb2754e949a09dc,
       5ac5d53983d45353bc6a9c54,
       5ac62eeca5421e4cb9abf63e]
},
{ _id: 5b9251f8ae8db624755f4b90,
 companies:
     [ 5b461c892bb9c81bd3ed4a25,
       5b5086196947782fbc873d28,
       5b76a6c79dc71a4a12564cc5 ]
}]

The final array should look like --

 [ 5ab20bb69cb2754e949a09dc,
   5ac5d53983d45353bc6a9c54,
   5ac62eeca5421e4cb9abf63e,
   5b461c892bb9c81bd3ed4a25,
   5b5086196947782fbc873d28,
   5b76a6c79dc71a4a12564cc5]

My code--

    Model.find().exec(function(err,gdoc){
          if(err)
          {
             callback({err:err,message:"Error looking up company"});
          }else
          {
             for (var i = 0, len = gdoc.length; i < len; i++) {                    
                    console.log(gdoc.companies);
              }
          }
    });

I am getting undefined values.

Any help is highly appreciated. Thanks in advance.

you are missing one closing curly bracket for for loop. not solution but just saying — Nimitt Shah
– Nimitt Shah, Commented Sep 12, 2018 at 13:46

str · Accepted Answer · 2018-09-12 14:11:42Z

2

The reason why you are getting undefined is that you try to access the non-existing companies property on gdoc. Instead of gdoc.companies, you have to use gdoc[i].companies.

Instead of your loop, you can use Array.prototype.concat together with the spread syntax (...) and Array.prototype.map as follows:

const gdoc = [
  {
    _id: '5366e9049cfc825b32966852',
    companies: [
      '5ab20bb69cb2754e949a09dc',
      '5ac5d53983d45353bc6a9c54',
      '5ac62eeca5421e4cb9abf63e',
    ],
  },
  {
    _id: '5b9251f8ae8db624755f4b90',
    companies: [
      '5b461c892bb9c81bd3ed4a25',
      '5b5086196947782fbc873d28',
      '5b76a6c79dc71a4a12564cc5',
    ],
  },
];

const companies = [].concat(...gdoc.map(doc => doc.companies));
console.log(companies);

edited Sep 12, 2018 at 14:11

answered Sep 12, 2018 at 13:55

str

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1 Comment

Prithviraj Mitra Over a year ago

Brilliant. The only thing which I was getting is a red mark under three dots. Then I change the ES version in my editor and all good. Thanks a lot.

Shilly · Accepted Answer · 2018-09-12 13:48:26Z

Basically you're trying to concatenate all the company fields of the results array. As long as you know that the key is companies, this is an easy reduction.

Arrays have a couple of builtin methods that make transforming them very easy, compared to having to use a for-loop.

Array.forEach(), Array.map(), Array.reduce() and Array.find() are the most frequently used ones.

//  Since these id's contain letters as well, they need to be strings.
const data = [
  {
    _id: "5366e9049cfc825b32966852",
    companies:[
      "5ab20bb69cb2754e949a09dc",
      "5ac5d53983d45353bc6a9c54",
      "5ac62eeca5421e4cb9abf63e"
    ]
  },
  {
    _id: "5b9251f8ae8db624755f4b90",
   companies:[
    "5b461c892bb9c81bd3ed4a25",
    "5b5086196947782fbc873d28",
    "5b76a6c79dc71a4a12564cc5"
    ]
  }
];

const companies = data.reduce(( result, item ) => result.concat( item.companies ), []);

console.log( companies );

Adrian · Accepted Answer · 2018-09-12 13:52:23Z

0

You can use the following method:

const map = [...[].concat(...arr.map((o) => o.companies))]

var arr = [ { _id: "5366e9049cfc825b32966852",
 companies:
     [ "5ab20bb69cb2754e949a09dc",
       "5ac5d53983d45353bc6a9c54",
       "5ac62eeca5421e4cb9abf63e"]
},
{ _id: "5b9251f8ae8db624755f4b90",
 companies:
     [ "5b461c892bb9c81bd3ed4a25",
       "5b5086196947782fbc873d28",
       "5b76a6c79dc71a4a12564cc5" ]
}];


const map = [...[].concat(...arr.map((o) => o.companies))]

console.log(map);

answered Sep 12, 2018 at 13:52

Adrian

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Comments

phuzi · Accepted Answer · 2018-09-12 13:52:55Z

0

How about running a reduce over the array.

const model = [{
    _id: "5366e9049cfc825b32966852",
    companies: [
      "5ab20bb69cb2754e949a09dc",
      "5ac5d53983d45353bc6a9c54",
      "5ac62eeca5421e4cb9abf63e"
    ]
  },
  {
    _id: "5b9251f8ae8db624755f4b90",
    companies: [
      "5b461c892bb9c81bd3ed4a25",
      "5b5086196947782fbc873d28",
      "5b76a6c79dc71a4a12564cc5"
    ]
  }
];

const reducer = (acc, value) => {
  acc.push(...value.companies);
  return acc;
};

console.log(model.reduce(reducer, []));

answered Sep 12, 2018 at 13:52

phuzi

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Comments

José Alves Durand Neto · Accepted Answer · 2018-09-12 13:59:28Z

0

You can do some thing like that!

var docs= [ { _id: "5366e9049cfc825b32966852",
 companies:
     [ "5ab20bb69cb2754e949a09dc",
       "5ac5d53983d45353bc6a9c54",
       "5ac62eeca5421e4cb9abf63e"]
},
{ _id: "5b9251f8ae8db624755f4b90",
 companies:
     [ "5b461c892bb9c81bd3ed4a25",
       "5b5086196947782fbc873d28",
       "5b76a6c79dc71a4a12564cc5" ]
}];
// your companies will be put in the folowing variable
var companies = [];

for ( var doc of docs){
    for (var item of doc.companies){
        companies.push(item)
    }
}

console.log(companies)

answered Sep 12, 2018 at 13:59

José Alves Durand Neto

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Comments

LKing · Accepted Answer · 2018-09-12 14:25:12Z

const data = [ { _id: '5366e9049cfc825b32966852',
 companies:
     [ '5ab20bb69cb2754e949a09dc',
       '5ac5d53983d45353bc6a9c54',
       '5ac62eeca5421e4cb9abf63e']
},
{ _id: '5b9251f8ae8db624755f4b90',
 companies:
     [ '5b461c892bb9c81bd3ed4a25',
       '5b5086196947782fbc873d28',
       '5b76a6c79dc71a4a12564cc5' ]
}]
let outputArr = []
data.map(d => outputArr.push(d.companies));
//Flatten
console.log([].concat.apply([],outputArr))

Both flatMap and flat which are currently an 'experimental technology' will allow a cleaner approach to this problem in the future. See:

Array.prototype.flat(): https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat

Array.prototype.flatMap(): https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flatMap

mankowitz · Accepted Answer · 2018-09-12 13:47:44Z

-1

You want something like this:

var k = [{
    _id: "5366e9049cfc825b32966852",
    companies: ["5ab20bb69cb2754e949a09dc",
      "5ac5d53983d45353bc6a9c54",
      "5ac62eeca5421e4cb9abf63e"
    ]
  },
  {
    _id: "5b9251f8ae8db624755f4b90",
    companies: ["5b461c892bb9c81bd3ed4a25",
      "5b5086196947782fbc873d28",
      "5b76a6c79dc71a4a12564cc5"
    ]
  }
];

var res = [];
k.forEach(function(id) {
  res.push(...id.companies)
});


console.log(res);

answered Sep 12, 2018 at 13:47

mankowitz

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2 Comments

Baruch Over a year ago

This returns an array of arrays, OP wants an array of strings

Shilly Over a year ago

This does not return an array of arrays since the three dots will spread the companies array into multiple values and array.push() accepts multiple arguments. My question would be, why use forEach() to mimic reduce() ?

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