Compare object with an array

Question

I've an object and the array as shown below and I wanted to remove all the properties of the object except those listed in the array. Can someone help me with a good lodash function to do this.

object : {A:1,B:2,C:3,D:4} 
array: [{type:B,value:xyz,order:1},{type:D,value:abc,order:0}]

I want the object to be {B:2,D:4} after the operation

@Kinduser, thanks for the response. I know how to do it in pure js, but I'm looking for a solution using lodash as we've been using that in our project and wanted to learn the same. — Ajay Srikanth, Mar 13 '17 at 21:07
do you want to mutate the object, or just filter it, or does it not matter? — orion, Mar 13 '17 at 21:11
@orion, I want to mutate the object, so that the object contains only the fields that are present in array. — Ajay Srikanth, Mar 13 '17 at 21:14

ibrahim mahrir · Accepted Answer · 2017-03-13T22:57:43.530

3

Use _.pick like this:

var result = _.pick(object, array);

var object = {
  A: 1,
  B: 2,
  C: 3,
  D: 4
};

var array = ["B", "D"];

var result = _.pick(object, array);

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

EDIT:

You should first use _.map to get the keys and then use _.pick like this:

var result = _.pick(object, _.map(array, function(e) {
  return e.type;
}));

or using arrow functions like this:

var result = _.pick(object, _.map(array, e => e.type));

or even shorter using the iteratee argument like this:

var result = _.pick(object, _.map(array, "type"));

var object = {
  A: 1,
  B: 2,
  C: 3,
  D: 4
};

var array = [{type: "B", value: "xyz", order: 1}, {type: "D", value: "abc", order: 0}];

var result = _.pick(object, _.map(array, "type"));

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

edited Mar 13 '17 at 22:57

answered Mar 13 '17 at 21:13

ibrahim mahrir

31,174
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hi, ibrahim thanks for the answer. First of all my apologies, I missed the crucial part of my array at least I believe which I've modified now. I realized about that mistake in my question only after looking at your answer as I've already read about pick before posting my question. – Ajay Srikanth Mar 13 '17 at 21:22
@AjaySrikanth see the **EDIT** section above! – ibrahim mahrir Mar 13 '17 at 21:32
Thanks ibrahim. This is what I wanted. – Ajay Srikanth Mar 13 '17 at 21:48
you can shorten this with `var result = _.pick(object, _.map(array, 'type'));` – ryeballar Mar 13 '17 at 22:53
@ryeballar yeah even clearer, didn't know you can do that so thanks! – ibrahim mahrir Mar 13 '17 at 22:58
@AjaySrikanth See the last edit it's even shorter thanks to ryballar! – ibrahim mahrir Mar 13 '17 at 22:59

score 2 · Answer 2 · answered Mar 13 '17 at 21:42

2

You can use Object.assign(), Array.prototype.map() , spread element, computed property, to assign result of filtering type properties to object

var object = {A:1,B:2,C:3,D:4} 
var array = [{type:"B",value:"xyz",order:1},{type:"D",value:"abc",order:0}];
object = Object.assign({}, ...array.map(({type}) => ({[type]:object[type]})));

console.log(object);

answered Mar 13 '17 at 21:42

guest271314

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what is the ... in Object.assign() ? Could you please explain that syntax. I've just started as full time js developer. I'm having trouble understanding few syntax here and there. – Ajay Srikanth Mar 13 '17 at 21:50
@AjaySrikanth See [What is SpreadElement in ECMAScript documentation? Is it the same as Spread operator at MDN?](http://stackoverflow.com/questions/37151966/what-is-spreadelement-in-ecmascript-documentation-is-it-the-same-as-spread-oper) – guest271314 Mar 13 '17 at 21:52

Matt D. Webb · Answer 3 · 2017-03-14T09:32:36.127

0

You can use _.pick along with _.map to achieve this:

let obj = { A:1, B:2, C:3, D:4 };
let arr = [{ type:'B', value:'xyz', order:1 },{ type:'D', value:'abc', order:0 }];

let output = _.pick(obj, _.map(arr, 'type'));

console.log(output); // { B:2, D: 4 }

Example: JsFiddle

Lodash Docs:

_.map(): link

_.pick(): link

edited Mar 14 '17 at 09:32

answered Mar 13 '17 at 21:35

Matt D. Webb

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Check the desired output again! – ibrahim mahrir Mar 13 '17 at 21:36
@ibrahimmahrir Ah pants! :-) – Matt D. Webb Mar 13 '17 at 21:37

Compare object with an array

3 Answers3

Lodash Docs: