Find difference in Objects using underscore.js

Question

So I have two JSON objects and I am trying to find difference between them using underscore js. However for some reason its returning me the whole object instead of just returning the difference. My goal here is to get the pattern back as its the only thing different.

var a = {
        "name":"donor",
        "label":"Donor Data File (donor)",
        "pattern":"^donor(\\.[a-zA-Z0-9]+)?\\.txt(?:\\.gz|\\.bz2)?$"
};
var b = {
         "name":"donor",
         "label":"Donor Data File (donor)",
         "pattern":"^donor(\\.[a-zA-Z0-9]+)?\\.txt(?:\\.gz)?$"
};

console.log(_.difference(a,b));

Am I not understanding the use case of _.difference properly? Heres a JSFiddle in case needed.

_.difference is for arrays; it sounds more like you want a full-on object diffing solution. E.g., github.com/flitbit/diff (Well, that's a bad example, but the libraries you seek exist.) — Dave Newton
– Dave Newton, Commented Jul 29, 2016 at 18:56

Thierry D. · Accepted Answer · 2018-03-28 01:14:57Z

5

/**
 * Deep diff between two object, using underscore
 * @param  {Object} object Object compared
 * @param  {Object} base   Object to compare with
 * @return {Object}        Return a new object who represent the diff
 */
const difference = (object, base) => {
  const changes = (object, base) => (
    _.pick(
      _.mapObject(object, (value, key) => (
        (!_.isEqual(value, base[key])) ?
          ((_.isObject(value) && _.isObject(base[key])) ? changes(value, base[key]) : value) :
          null
      )),
      (value) => (value !== null)
    )
  );
  return changes(object, base);
}

edited Mar 28, 2018 at 1:14

answered Mar 28, 2018 at 1:08

Thierry D.

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1 Comment

codelovesme Over a year ago

Perfect solution !

Community · Accepted Answer · 2017-05-23 11:51:44Z

1

_.difference is meant to compare arrays, you're comparing objects. See this answer: using underscore's “difference” method on arrays of objects

edited May 23, 2017 at 11:51

CommunityBot

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answered Jul 29, 2016 at 18:55

Caius

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Comments

Aren Hovsepyan · Accepted Answer · 2016-07-29 19:16:29Z

0

Underscore has method isMatch,but no method that will return difference for objects, that takes 2 as parameter Objects and match their properties

var stooge = {name: 'moe', age: 32};
_.isMatch(stooge, {age: 32});

you can create your own implementation

function getDiffProperties(object1,object2){
      var difference  = [];
  
      for(key in object1){
        if(object1[key] != object2[key]){
          difference.push(key)
        }
      }

      for(key in object2){
        if(object1[key] != object2[key]){
          difference.push(key)
        }
      }
     
     return difference
}

console.log(getDiffProperties({name: 'moe', age: 32},{age: 32}))

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

edited Jul 29, 2016 at 19:16

answered Jul 29, 2016 at 18:55

Aren Hovsepyan

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1 Comment

Dave Newton Over a year ago

Match returns a boolean, though. OP is trying to get an object back that has the same shape as only the differing fields.

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