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I want to find the matching values between two arrays and create a json array setting true if the values matched or false if they didn't. I know, that the values in the secondArray will always match some values from the first array and that it will always be smaller, because the secondArray is created based on the first one.

let firstArray = ["One", "Two", "Three", "Four", "Five"];
let secondArray = ["Three", "Four"];
let jsonArray = [];

I want to create a json array:

[
  {
    "name": "One",
    "matched": false
  },
  {
    "name": "Two",
    "matched": false
  },
  {
    "name": "Three",
    "matched": true
  },
  {
    "name": "Four",
    "matched": true
  },
  {
    "name": "Five",
    "matched": false
  }
]

Normally, I would do something like this:

            firstArray.forEach(firstElement=>{
              secondArray.forEach(secondElement=>{
                  if(firstArray.indexOf(secondElement)>=0){
                      jsonArray.push({'name': secondElement, 'matched': true});
                  }else{
                      jsonArray.push({'name': secondElement, 'matched': false});
                  }
              });
          });

But this just creates a json array with duplicated values where the name is the same, but the matched value are falsed and true.

It seems like I'm getting lost in something very simple.

I want to find the matching values between two arrays and create a json array setting true if the values matched or false if they didn't. I know, that the values in the secondArray will always match some values from the first array and that it will always be smaller, because the secondArray is created based on the first one.

let firstArray = ["One", "Two", "Three", "Four", "Five"];
let secondArray = ["Three", "Four"];
let jsonArray = [];

I want to create a json array:

[
  {
    "name": "One",
    "matched": false
  },
  {
    "name": "Two",
    "matched": false
  },
  {
    "name": "Three",
    "matched": true
  },
  {
    "name": "Four",
    "matched": true
  },
  {
    "name": "Five",
    "matched": false
  }
]

Normally, I would do something like this:

            firstArray.forEach(firstElement=>{
              secondArray.forEach(secondElement=>{
                  if(firstArray.indexOf(secondElement)>=0){
                      jsonArray.push({'name': secondElement, 'matched': true});
                  }else{
                      jsonArray.push({'name': secondElement, 'matched': false});
                  }
              });
          });

But this just creates a json array with duplicated values where the name is the same, but the matched value are falsed and true.

It seems like I'm getting lost in something very simple.

• javascript
• arrays
• typescript
• match

Share Improve this question Follow edited Jun 20, 2018 at 16:05 Shift 'n Tab 9,4531414 gold badges7979 silver badges123123 bronze badges asked Jun 20, 2018 at 14:33 siesie 16111 gold badge44 silver badges1919 bronze badges 2

• you have a lot of typos in your code – Philipp Sander Commented Jun 20, 2018 at 14:37
• you have to merge both array and set matched to false, then ou have to intersect both array and set values from the intersect to matched true in your merged array – Philipp Sander Commented Jun 20, 2018 at 14:38

Add a ment  | 

6 Answers 6

Sorted by: Reset to default 3

You can use the bination of map and includes helper to achieve that.

let firstArray = ["One", "Two", "Three", "Four", "Five"];
let secondArray = ["Three", "Four"];
let jsonArray = [];

jsonArray = firstArray.map(i => {
   return { 'name': i, 'matched': secondArray.includes(i) };
});

console.log(jsonArray);

All the other solutions here perform unnecessary putations; their run-time grows with the square of the array length. Try running them with arrays of size 100k+ :-)

The solution you are looking for is quite simple and runs in O(n):

let firstArray = ["One", "Two", "Three", "Four", "Five"];
let secondArray = ["Three", "Four"];

let map = {};
firstArray.forEach(i => map[i] = false);
secondArray.forEach(i => map[i] === false && (map[i] = true));
let jsonArray = Object.keys(map).map(k => ({ name: k, matched: map[k] }));

Try this:

  let firstArray = ["One", "Two", "Three". "Four", "Five"];
  let secondArray = ["Three", "Four"];
  let jsonArray = [];
  firstArray.forEach(firstElement=>{
        if(secondArray.indexOf(firstElement)>=0){
            jsonArray.push({'name': firstElement, 'matched': true});
        }else{
            jsonArray.push({'name': firstElement, 'matched': false});
        }
 });

Hope this code will help you

We can use

Array.prototype.includes()

to check if an element exist or not in an array

let firstArray = ["One", "Two", "Three", "Four", "Five"];
let secondArray = ["Three", "Four"];
let jsonArray = [];

firstArray.forEach(val => {
    if (secondArray.includes(val)) {
        jsonArray.push({
            'name': val,
            'matched': true
        })

    } else {
        jsonArray.push({
            'name': val,
            'matched': false
        })
    }

})

console.log(jsonArray);

use th find to check element exist

firstArray.forEach(secondElement=>{
  let exist = secondArray.find((item) => item === secondElement);
  if(exist){
    jsonArray.push({'name': secondElement, 'matched': true})
  }else{

    jsonArray.push({'name': secondElement, 'matched': false})
  }
});

Demo

You can do this in two way.

Way1:
let array1 = ['a','b','c','d'];
let array2 = ['b','d'];
let monArray = [];

array1.forEach( x => {
    if(array2.indexOf(x) != -1){
      monArray.push(x);
    }
});`

console.log(monArray);   //monArray is the resulting array

Way2: Use intersection of Underscore.js

At first you have to import underscore:  
import * as _ from 'underscore';`  

Then use intersection to calculate mon.  
monArray = _.intersection(array1, array2);

console.log(monArray);   //monArray is the resulting array

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