how to update an array element property with another array element property in underscore.js

Question

First array

userData = [
    { name: abc, age: 24 },
    { name: ghi, age: 22 },
    { name: tyu, age: 20 }
];

Second array

userAge = [
    { age: 25 },
    { age: 26 },
    { age: 22 }
];

Both arrays have the same length.

How do I update the useData[0].age with userAge[0] using Underscore.js?

If you are satisfied with one of the answers, please accept it. You could also add your own answer if the existing one is incomplete / incorrect @Debashrita — martianwars, Dec 28 '16 at 08:01

martianwars · Answer 1 · 2016-12-03T10:15:13.787

0

Since you need to do this over a list of dictionaries, you will need to iterate over the list using _.each.

Something like this will help,

_.each(userData, function(data, index) {
    data.age = userAge[index].age;
});

edited Dec 03 '16 at 10:15

answered Dec 03 '16 at 06:40

martianwars

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To just update one element, why do you need `underscore.js`? You can just do `userData[0].age = userAge[0].age` right? – martianwars Dec 03 '16 at 06:50
not one element i gave an exapmle . we need to update userData[i].age = userAge[i].age – Debashrita Dec 03 '16 at 06:58
1

As you're mutating `userData` you might as well use `_.each` rather than `_.map` – Gruff Bunny Dec 03 '16 at 09:40

score 0 · Answer 2 · edited May 23 '17 at 11:46

While @martianwars is correct, it could be a little more generic, thus more useful, if it could apply any attribute.

Say we have an array of changes to apply, with each not being necessarily the same attribute or even multiple attributes per object:

var changes = [
    { age: 25 },
    { name: "Guy" },
    { name: "Pierre", age: 22 }
];

Changes could be applied with _.extendOwn

_.each(userData, function(data, index) {
    _.extendOwn(data, changes[index]);
});

Proof of concept:

var userData = [{
  name: "abc",
  age: 24
}, {
  name: "ghi",
  age: 22
}, {
  name: "tyu",
  age: 20
}];

var changes = [{
  age: 25
}, {
  name: "Guy"
}, {
  name: "Pierre",
  age: 22
}];


_.each(userData, function(data, index) {
  _.extendOwn(data, changes[index]);
});

console.log(userData);

<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script>

This will only work if the arrays are in sync. Meaning that if there are 4 objects in the userData array, and only 3 changes, they need to be at the right index and that could become a problem.

A solution to this is to have an identification property, often represented by an id attribute.

userData = [
    { id: '1', name: 'abc', age: 24 },
    { id: '2', name: 'ghi', age: 22 },
    { id: '3', name: 'tyu', age: 20 }
];

See Merge 2 objects based on 1 field using Underscore.js for details.

how to update an array element property with another array element property in underscore.js

2 Answers2