lodash filter by property array of array

Question

I have array of users who have a property array 'rights' and I want to filter out the users who have specific rights. I would like to filter by an array so if I wanted all the users with full rights ['full'] or users with both full and edit ['full','edit']. I am fairly new to using lodash and I think I can chain some together but I am not sure if this is there are more efficient ways of doing it.

Here is my plunker: http://plnkr.co/edit/5PCvaDJaXF4uxRowVBlK?p=preview

Result ['full'] :

[{
    "name": "Company1 Admin",
    "rights": [
      "full"
    ]
  },
  {
    "name": "FullRights Company1",
    "rights": [
      "full","review"
    ]
  }]

Result ['full','edit']:

[{
    "name": "Company1 Admin",
    "rights": [
      "full"
    ]
  },
  {
    "name": "FullRights Company1",
    "rights": [
      "full","review"
    ]
  },
  {
    "name": "EditRights Company1",
    "rights": [
      "edit"
    ]
  }]

Code:

var users = [
      {
        "name": "Company1 Admin",
        "rights": [
          "full"
        ]
      },
      {
        "name": "FullRights Company1",
        "rights": [
          "full","review"
        ]
      },
      {
        "name": "ApproveRights Company1",
        "rights": [
          "approve","review"
        ]
      },
      {
        "name": "EditRights Company1",
        "rights": [
          "edit"
        ]
      },
      {
        "name": "ReviewRights Company1",
        "rights": [
          "review"
        ]
      },
      {
        "name": "NoRights Company1",
        "rights": [
          "none"
        ]
      }
    ];
        
var tUsers = [];
var filterRights = ['full','edit'];
_.forEach(users, function(user) {
    if (_.intersection(user.rights, filterRights).length > 0) {
      tUsers.push(user);
    }
}) ;        
        
//console.log('users', JSON.stringify(users, null, 2)); 
console.log('tUsers', JSON.stringify(tUsers, null, 2));

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.10.1/lodash.min.js"></script>

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

From the docs

_.filter(collection, predicate, thisArg);

Arguments

collection (Array|Object|string): The collection to iterate over.

[predicate=_.identity] (Function|Object|string): The function invoked per iteration.

[thisArg] (*): The this binding of predicate.

Chaining is great when you want to connect different processing steps.

If your problem statement was to

filter by rights
sort by oldest person
take 10

Then chaining would make a lot of sense.

This problem seems to be mostly custom logic on filtering.

var users = [/* Your user data here */];
function filterByRights (users, rights) {
    return _.filter(users, function (user) {
        return _.any(user.rights, function (right) {
            return _.contains(rights, right);
        });
    });
}
filterByRights(users, ['full', 'edit']); // [/*Users with full or edit rights*/]

I think my example is good becuase it doesn't depend on conditional logic. It uses lodash defined methods like any and contains

Performance concerns

I want to expand on what performance concerns you have. Here are a couple of points.

Your question code is maintaining its own mechanism for filtering out users. While it is a perfectly good solution you should opt into letting the guys who maintain lodash handle this logic. They have probably spent a lot of time optimizing how to create another array from an original one.
_.any is more efficient than _.intersection. _.intersection needs to process every element to know what the intersection is. _.any stops when it hits the first element which passes the predicate otherwise it checks each of them. This point is minor since there are a small number of "rights"
The example I've given is probably more "lodash standard". You typically can do data transformations completely with lodash defined methods and trivial predicates.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Dec 24, 2015 at 1:16

t3dodson

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3 Comments

Enkode Over a year ago

Thanks for the great response. Do you think this will be faster than using forEach and intersection? I have not done any javascript benchmarking but this will get run a lot and speed is a factor.

t3dodson Over a year ago

Hey I'm glad to help. From a big oh perspective. _.foreach is equivalent to _.filter(it simply iterates over a list performing an action on each element). _.any is more efficient than _.intersect becuase _.intersect has to process all of the rights. I would expect that this runs faster too because it doesn't have the memory overhead of creating a new array which is probably very costly.

Enkode Over a year ago

Thanks I will mark your answer as correct if but I would like to get some more feedback first. Thanks again.

chonz0 · Accepted Answer · 2017-01-09 14:20:16Z

3

Here is an update to @t3dodson 's answer. You should now use the following snippet if using current (4.17.4) Lodash version:

function filterByRights (users, rights) {
  return _.filter(users, function (user) {
    return _.some(user.rights, function (right) {
      return _.includes(rights, right);
    });
  });
}

From the Changelog:

Removed _.contains in favor of _.includes

Removed _.any in favor of _.some

answered Jan 9, 2017 at 14:20

chonz0

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Comments

Adam Boduch · Accepted Answer · 2015-12-24 14:17:32Z

1

I think you were on the right path with intersection() (I've never seen any performance issues with this function). Here's how I would compose an iteratee using flow():

_.filter(users, _.flow(
    _.property('rights'), 
    _.partial(_.intersection, filterRights), 
    _.size
));

The property() function gets the rights property, and passes it to intersection(). We've already partially-applied the filterRights array. Lastly, the size() function is necessary to pass a thruthy/falesy value to filter().

answered Dec 24, 2015 at 14:17

Adam Boduch

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1 Comment

Enkode Over a year ago

Thanks Adam, I will review this and possible run some stress testing on a couple different methods.

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