arrays - Nested forEach loops to add object to existing object javascript - Stack Overflow

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Is there a better way to iterate over two array of objects than what I have done below? It seems messy to do it this way. I'm using lodash.

var array1 = [
   {id:4356, name: 'James', sex: 'male'}, 
   {id:7899, name: 'Jimmy', sex: 'male'}, 
   {id:2389, name: 'Dawn', sex: 'female'}
];

var array2 = [
    {id:4356, salary: 1000, job: 'programmer'}, 
    {id:7899, salary: 2000, job: 'tester'}, 
    {id:2389, salary: 3000, job: 'manager'}
];

Example output:

console.log(array1[0])
{
    id:4356, 
    name: James, 
    sex: male, 
    person: {
        id:4356, 
        salary: 1000, 
        job: programmer
    }
}

Function:

_.forEach(array1, function(item1) {
    _.forEach(array2, function(item2) {
       if(item1.id === item2.id){
          item1.person = item2;
        }
     });
});

Is there a better way to iterate over two array of objects than what I have done below? It seems messy to do it this way. I'm using lodash.

var array1 = [
   {id:4356, name: 'James', sex: 'male'}, 
   {id:7899, name: 'Jimmy', sex: 'male'}, 
   {id:2389, name: 'Dawn', sex: 'female'}
];

var array2 = [
    {id:4356, salary: 1000, job: 'programmer'}, 
    {id:7899, salary: 2000, job: 'tester'}, 
    {id:2389, salary: 3000, job: 'manager'}
];

Example output:

console.log(array1[0])
{
    id:4356, 
    name: James, 
    sex: male, 
    person: {
        id:4356, 
        salary: 1000, 
        job: programmer
    }
}

Function:

_.forEach(array1, function(item1) {
    _.forEach(array2, function(item2) {
       if(item1.id === item2.id){
          item1.person = item2;
        }
     });
});

• javascript
• arrays
• object
• lodash

Share Improve this question Follow edited Jan 15, 2016 at 13:05 Adam Boduch 11.2k33 gold badges3232 silver badges3838 bronze badges asked Jan 14, 2016 at 19:39 tester123tester123 1,12322 gold badges1212 silver badges1818 bronze badges 3

• Convert one of the arrays into an id -> person map first? – Felix Kling Commented Jan 14, 2016 at 19:42
• Possible duplicate of Functional way of joining two js object arrays based on mon id – nograde Commented Jan 14, 2016 at 19:57
• Gruff Bunny's answer (linked above) is pretty prehensive. – nograde Commented Jan 14, 2016 at 19:59

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 6

Since you're using lodash, you could use the _.find() method to find the corresponding object in array2 based on the id properties.

_.forEach(array1, function(item1) {
    item1.person = _.find(array2, {id: item1.id});
});

It's worth pointing out that this will result in an undefined person property if an object isn't found. If that's a problem, simply check to see if an object is returned:

_.forEach(array1, function(item1) {
    var obj = _.find(array2, {id: item1.id});
    if (obj) {
        item1.person = obj;
    }
});

Without lodash, it would be pretty similar:

array1.forEach(function(item1) {
    item1.person = array2.find(function (item2) {
      return item2.id === item1.id;
    });
});

I would build a reference object and add to it, that way you're not loading the second array N times. Something like this:

    var array1 = [{id:4356, name: 'James', sex: 'male'}, 
        {id:7899, name: 'Jimmy', sex: 'male'}, 
        {id:2389, name: 'Dawn', sex: 'female'}
    ];

    var array2 = [{id:4356, salary: 1000, job: 'programmer'}, 
        {id:7899, salary: 2000, job: 'tester'}, 
        {id:2389, salary: 3000, job: 'manager'}
    ];

    var array3 = {};

    for(var i in array1) {
        array3[array1[i]['id']] = array1[i];
    }

    for(var i in array2) {
        for(var key in array2[i]) {
            array3[array2[i]['id']][key] = array2[i][key];
        }
    }

This gives you an object with the properties of both arrays like:

    Object {2389: Object, 4356: Object, 7899: Object}

With the benefit that you only iterate over each array once.

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