I am trying to use the _.without and _.difference methods in the underscore.js library with no luck.

Here is some code.

var someIds = _.pluck(parsedID1, 'id');
var otherIds = _.pluck(parsedID2, 'id);

Here is where the trouble starts, I want to remove all of the otherIds out of the someId's list. So I have two options according to the website, either I can use _.difference || _.without. I use them like so...

var newArray = _.without(_.toArray(someIds), _.toArray(otherIds));

I have also tried to do this with _.difference as well, but I cant seem to get the methods to do anything other than return a copy of the first argument into the function. I have also tried passing the arguments into the functions without using the _.toArray() but the same thing happens.Has anyone ever encountered this error before?

EDIT:

I have tried the way as proposed below. I will give some more code in hopes of fixing this.

The arrays that I am passing in as arguments are in the following format.

var array = ['100004191488120', '100004191488321'];

When I pass into the _.difference I do as follows:

var newArray = _.difference(someIds, otherIds);

If someIds length is 657 and otherIds is 57 I should be getting a result of 600 Id's. Instead I get a result of whatever the length of the first argument is, being 657.

EDIT 2: Solved

I figured out what the problem was, after all that frustration the problem lied with the second argument to difference I was passing in.

I was doing a db query and getting back a list that looked like the following.

[{ _id: 514721152222111116666777, facebook: { id: '123456789' } },
 { _id: 514721152222111116666778, facebook: { id: '12345678' } },]

After I received those results I wanted to get the facebook id so I did the following,

var array = _.pluck(users, 'facebook.id');

Thats were the problem was, that pluck was sending me back a list of undefined. Instead I had to do 2 plucks before instead of one, like the following.

var temp = _.pluck(users, 'facebook'); 
var arrayId = _.pluck(temp, 'id');

Thanks @ZenMaster for dropping the knowledge on the difference between _.without && _.difference. Your answer was correct, was pretty brain-dead after a binder and didn't see the obvious.

I am trying to use the _.without and _.difference methods in the underscore.js library with no luck.

Here is some code.

var someIds = _.pluck(parsedID1, 'id');
var otherIds = _.pluck(parsedID2, 'id);

Here is where the trouble starts, I want to remove all of the otherIds out of the someId's list. So I have two options according to the website, either I can use _.difference || _.without. I use them like so...

var newArray = _.without(_.toArray(someIds), _.toArray(otherIds));

I have also tried to do this with _.difference as well, but I cant seem to get the methods to do anything other than return a copy of the first argument into the function. I have also tried passing the arguments into the functions without using the _.toArray() but the same thing happens.Has anyone ever encountered this error before?

EDIT:

I have tried the way as proposed below. I will give some more code in hopes of fixing this.

The arrays that I am passing in as arguments are in the following format.

var array = ['100004191488120', '100004191488321'];

When I pass into the _.difference I do as follows:

var newArray = _.difference(someIds, otherIds);

If someIds length is 657 and otherIds is 57 I should be getting a result of 600 Id's. Instead I get a result of whatever the length of the first argument is, being 657.

EDIT 2: Solved

I figured out what the problem was, after all that frustration the problem lied with the second argument to difference I was passing in.

I was doing a db query and getting back a list that looked like the following.

[{ _id: 514721152222111116666777, facebook: { id: '123456789' } },
 { _id: 514721152222111116666778, facebook: { id: '12345678' } },]

After I received those results I wanted to get the facebook id so I did the following,

var array = _.pluck(users, 'facebook.id');

Thats were the problem was, that pluck was sending me back a list of undefined. Instead I had to do 2 plucks before instead of one, like the following.

var temp = _.pluck(users, 'facebook'); 
var arrayId = _.pluck(temp, 'id');

Thanks @ZenMaster for dropping the knowledge on the difference between _.without && _.difference. Your answer was correct, was pretty brain-dead after a binder and didn't see the obvious.

• javascript
• node.js
• underscore.js

1 Answer 1

1. You don't need an _.toArray on the first argument of the without function
2. The second (and more) arguments to the without is not an array - it's a "list" of values.

The proper call would be:

var newArray = _.without(['1', '2', '3'], '1', '3');

which would result in:

['2']

In your case, you'd have to use _.difference as can be seen on JSFiddle here.

Here is the code:

var parsedID1 = [{id: '1', name: 'name1'}, {id: '2', name: 'name2'}];
var parsedID2 = [{id: '1', name: 'name1'}, {id: '3', name: 'name3'}];

var someIds = _.pluck(parsedID1, 'id');
var otherIds = _.pluck(parsedID2, 'id');

console.log(someIds, otherIds);

var newArray = _.difference(someIds, otherIds);

console.log(newArray);