node/angular js how to find null attributes in an array of objects

Question

Is there a better way to do this in lodash? I am basically trying to find all the keys that have null values.

var data = [
  { user: 'John', pos: null },
  { user: 'Tim', age: 40 },
  { user: 'Dave', age: null }
];
$scope.parsed = [];
_.each(data, function(obj) {
  _.each(_.keys(obj), function(k){
    if (obj[k] === null) {
      $scope.parsed.push(k);
    }
  })
});
console.info($scope.parsed);

Output: ["pos","age"]

Thanks!

What is the problem with that? Legibility? Optimization issues? Bear in mind that if there is a predefined lodash function it will very likely do the same: Cycle through the array, through each key to determine if it is null. I think that _.filter (lodash.com/docs#filter) would come useful, it "Iterates over elements of collection, returning an array of all elements predicate returns truthy for." — adelriosantiago
– adelriosantiago, Commented Nov 14, 2015 at 21:30
Agree with @adelriosantiago, there already is a lodash function for checking for null, _.null(value), which does the same thing you're doing above (just in a lodash way). — Andres I Perez
– Andres I Perez, Commented Nov 14, 2015 at 21:41

Oleksandr T. · Accepted Answer · 2015-11-14 21:44:24Z

1

Try this

var data = [
  { user: 'John', pos: null },
  { user: 'Tim', age: 40 },
  { user: 'Dave', age: null }
];

var result = _(data)
  .map(function (element) {
    return _.keys(_.pick(element, _.isNull));
  })
  .flatten()
  .value();

console.log(result);

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

edited Nov 14, 2015 at 21:44

answered Nov 14, 2015 at 21:31

Oleksandr T.

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1 Comment

Oleksandr T. Over a year ago

@user2994871 could you give feedback?

Simon H · Accepted Answer · 2015-11-14 21:34:27Z

0

Not sure how you define 'better', but I think this is a more functional answer - filter those elements that have a value that is null

$scope.parsed = _.filter(data, function(d) {
    return (_.values(d).indexOf(null) !== -1);
}

var data = [{
  user: 'John',
  pos: null
}, {
  user: 'Tim',
  age: 40
}, {
  user: 'Dave',
  age: null
}];

parsed = _.filter(data, function(d) {
      return (_.values(d).indexOf(null) !== -1);
    });
                        
console.log(parsed);

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

edited Nov 14, 2015 at 21:34

answered Nov 14, 2015 at 21:27

Simon H

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1 Comment

Oleksandr T. Over a year ago

Output should be ["pos","age"] not full objects

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