push a array object into another array object if the value not exists

Question

Need to push the array object(arr1) valeus into another array object(arr2) if the value not exist. The existing values will not push into another array.

var arr1 = [{
    name: 'fred'
}, {
    name: 'bill'
}, {
    name: 'ted'
}, {
    name: 'james'
}];

var arr2 = [{
    name: 'spil'
}, {
    name: 'fred'
}, {
    name: 'bill'
},{
    name: 'paul'
}, {
    name: 'stone'
}];

function add(name) {
    var found = arr1.some(function (el) {
      return el.name === name;
    });
    if (!found) {
        arr1.push(arr2);
    }
    return arr2;
}

Fiddle

You are talking about pushing values into arr2, but your code does the opposite (or sort of tries to). Given that your add() function seems to take a string as input, what should happen (a) if the value is currently in neither array? (b) If it is currently in only arr1? (c) If it is currently in only arr2? (d) If it is already in both arrays? — nnnnnn
– nnnnnn, Commented Jun 28, 2016 at 6:28

Yennefer · Accepted Answer · 2022-03-26 20:07:45Z

You could use a hash table for look up, if the name property is already in arr1. If not push the actual item to arr1.

var arr1 = [{ name: 'fred' }, { name: 'bill' }, { name: 'ted' }, { name: 'james' }],
    arr2 = [{ name: 'toString' }, { name: 'spil' }, { name: 'fred' }, { name: 'bill' }, { name: 'paul' }, { name: 'stone' }],
    hash = Object.create(null);

arr1.forEach(function (a) {
    hash[a.name] = true;
});
arr2.forEach(function (a) {
    hash[a.name] || arr1.push(a);
});

console.log(arr1);

PS

Just to make clear, why Object.create(null), a really empty object as hash and not {}, an empty object. Pay attention to the item { name: 'toString' }. In the first part, the item gets inserted, in the second not, because hash has a property with the name toString.

var arr1 = [{ name: 'fred' }, { name: 'bill' }, { name: 'ted' }, { name: 'james' }],
    arr2 = [{ name: 'toString' }, { name: 'spil' }, { name: 'fred' }, { name: 'bill' }, { name: 'paul' }, { name: 'stone' }],
    hash = {}; // now an object

arr1.forEach(function (a) {
    hash[a.name] = true;
});
arr2.forEach(function (a) {
    hash[a.name] || arr1.push(a);
});

console.log(arr1);

Jaydeep Gondaliya · Accepted Answer · 2016-06-28 06:27:33Z

1

If you're only appending a single variable, then push() works just fine. If you need to append another array, use concat(): var ar1 = [1, 2, 3]; var ar2 = [4, 5, 6];

var ar3 = ar1.concat(ar2);

alert(ar1);
alert(ar2);
alert(ar3);

Will spit out:

"1,2,3"
"4,5,6"
"1,2,3,4,5,6"

The concat does not affect ar1 and ar2 unless reassigned, for example:

ar1 = ar1.concat(ar2);
alert(ar1);

Will display:

"1,2,3,4,5,6"

answered Jun 28, 2016 at 6:27

Jaydeep Gondaliya

3216 silver badges17 bronze badges

Comments

Gayathri Mohan · Accepted Answer · 2016-06-28 06:29:15Z

1

Hi check this u can push the first array to other array later can use the underscore unique to return only the unique objects

   var arr1 = [{
    name: 'fred'
}, {
    name: 'bill'
}, {
    name: 'ted'
}, {
    name: 'james'
}];

var arr2 = [{
    name: 'spil'
}, {
    name: 'fred'
}, {
    name: 'bill'
}, {
    name: 'paul'
}, {
    name: 'stone'
}];

arr1.push(arr2);
arr1 = _.uniq(arr1, false, function(p) {
    return p.name;
});

answered Jun 28, 2016 at 6:29

Gayathri Mohan

2,9724 gold badges21 silver badges26 bronze badges

2 Comments

nnnnnn Over a year ago

And for the JS beginner who doesn't know what Underscore is? (Also, you're pushing the entire arr2 array as a single element of arr1 - I know the OP's code did this, but I don't think it's what they want.)

Gayathri Mohan Over a year ago

ha u started again @nnnnnn

Jack jdeoel · Accepted Answer · 2016-06-28 07:22:39Z

1

Use indexOf for get not exist name.Store first your arr1 name as a array !!!

var hasName = arr1.map(function(obj) { return obj.name; });
arr2.filter(function(v,i) { if(hasName.indexOf(v.name) == -1) arr1.push(v); });      
console.log(arr1);

edited Jun 28, 2016 at 7:22

answered Jun 28, 2016 at 7:13

Jack jdeoel

4,5886 gold badges28 silver badges57 bronze badges

Comments

Grgur · Accepted Answer · 2016-06-28 07:29:51Z

1

If you have the luxury of using ECMAScript 6 then you can create this lovely block

var arr1 = [{
    name: 'fred'
}, {
    name: 'bill'
}, {
    name: 'ted'
}, {
    name: 'james'
}];

var arr2 = [{
    name: 'spil'
}, {
    name: 'fred'
}, {
    name: 'bill'
},{
    name: 'paul'
}, {
    name: 'stone'
}];

arr2.forEach(arr2Item => arr1.find(({ name }) => name === arr2Item.name) || arr1.push(arr2Item));

console.log(arr1);

Given that there's plenty of recursion, you may want to store your data in a different format so you can compare more easily. You could use object hash or ES6 Map to make your life easier. Also to save a few cycles 😁

edited Jun 28, 2016 at 7:29

answered Jun 28, 2016 at 7:22

Grgur

7,4122 gold badges21 silver badges34 bronze badges

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