I'm using _.pluck() from lodash to get the value of the keys from an array.

var employees = [
  {
    Name : "abc"  
  },
  {
    Name : "xyz"
  }
]

var res = _.pluck(employees, 'Name'); 

Variable res would contain ['abc,'xyz']

When I do a search for some other field field

var res = _.pluck(employees, 'SomeRandomField');   

Result - [undefined, undefined]

How can I get the above result just as null of undefined instead of an array of undefined values

Plnkr :

I'm using _.pluck() from lodash to get the value of the keys from an array.

var employees = [
  {
    Name : "abc"  
  },
  {
    Name : "xyz"
  }
]

var res = _.pluck(employees, 'Name'); 

Variable res would contain ['abc,'xyz']

When I do a search for some other field field

var res = _.pluck(employees, 'SomeRandomField');   

Result - [undefined, undefined]

How can I get the above result just as null of undefined instead of an array of undefined values

Plnkr : http://plnkr.co/edit/qtmm6xgdReCuJP5fm1P2?p=preview

• javascript
• lodash

• just as null of undefined -> What do you mean by that? – thefourtheye Commented Feb 27, 2015 at 7:05
• i've updated with a plnkr when you run it in console you'll see [undefined,undefined] – user1184100 Commented Feb 27, 2015 at 7:08
• What do you want the expected output to be? – thefourtheye Commented Feb 27, 2015 at 7:09
• null or just undefined instead of it being in an array – user1184100 Commented Feb 27, 2015 at 7:11
• What if only one object doesn't have SomeRandomField and all others have that? – thefourtheye Commented Feb 27, 2015 at 7:11

3 Answers 3

You can use filter and pluck:

var res = _.filter(_.pluck(employees, 'Name'), function(item) {
    return item;
});

You can use pact() to remove falsey values from the plucked array. You can use thru() to alter the output of the wrapper. In this case, we want null if all the plucked values are undefined.

var collection = [ {}, {}, {} ];

_(collection)
    .pluck('foo')
    .pact()
    .thru(function(coll) { return _.isEmpty(coll) ? null : coll; })
    .value();
// → null

I looks like you're actually looking for the .some function:

var res = _.pluck(employees, "Name");
res = res.some(function (d) { return d }) ? // are any of the elements truth-y?
    // if so, map the  false-y items to null
    res.map(function (item) { return item || null; }) :
    // otherwise (no truth-y items) make res `null`
    null;

I took a look at the lodash documentation for .pluck and I don't believe that's possible.

_.pluck(collection, key)

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

key (string): The key of the property to pluck.

What you can instead do is .pluck then use JavaScript's builtin (or lodash's) .map:

var res = _.pluck(employees, 'Name').map(function (d) {
    return d ? d : null;
});

Which is rather inefficient. You might as well write your own function that only iterates over the array once:

_.nullPluck = function (arr, key) {
    return arr.map(function (d) {
        return d && d[key] ? d[key] : null;
    }) 
}