CODEWITHSUNDEEP
javascriptlodash
Asmor
Asmor

Reputation: 5181

Find properties of JS object with truthy values using lodash

Let's say I have an object like:

var foo = {
    alpha: true,
    beta: false,
    gamma: true
}

I can use _.findKey to get one key with a true value, but I'd really like to get an array containing all keys with a true value. E.g.

_.findAllKeys(foo, function(val) { return val; });
// yields -> ["alpha", "gamma"]

It's simple enough to write a function to do this, but it seems like such an obvious generalization of findKey that I feel I must just be missing it. Does lodash have such a function?

Upvotes: 14

Views: 18739

Answers (7)

Subrata Sarkar
Subrata Sarkar

Reputation: 121

We can use pickBy() in lodash to get the key for which value equal to true.

const active = _.keys(_.pickBy(foo));

Alternatively we can also use,

var active = _.keys(foo).filter(function (id) {
    return foo[id]
});

Upvotes: 5

Walter Zalazar
Walter Zalazar

Reputation: 541

Just try 

var foo = {
    alpha: true,
    beta: false,
    gamma: true
}

_.pickBy(foo, _.identity);

Upvotes: 2

Vincent van der Weele
Vincent van der Weele

Reputation: 13177

I personally prefer the following - even though it is more verbose - because I think it is more obvious what it does. It requires es6 syntax, though:

_.toPairs(foo)
  .filter([key, value] => value)
  .map([key, value] => key);

If your ESLint does not allow unused variables you can for instance use the following in .eslint.yml:

rules:    
  no-unused-vars:
    - 2
    - vars: all
      args: after-used
      argsIgnorePattern: _$

Which allows to write

_.toPairs(foo)
  .filter([key_, value] => value)
  .map([key, value_] => key);

Upvotes: 0

Adam
Adam

Reputation: 571

pickBy in loDash by default uses _.identity to filter properties so you can use it like this:

_.pickBy({'a': undefined, 'b':1, c:{}});

// => Object {b: 1, c: Object}

Upvotes: 4

dting
dting

Reputation: 39287

var foo = {
    alpha: true,
    beta: false,
    gamma: true
};

var t1 = _.keys(_.pick(foo, _.identity));
console.log(t1);

var t2 = _(foo).pick(_.identity).keys().value();
console.log(t2);
<script type="text/javascript" src="//cdnjs.cloudflare.com/ajax/libs/lodash.js/3.5.0/lodash.min.js"></script>
<script src="https://getfirebug.com/firebug-lite-debug.js"></script>

Edit:
As noted by @backdesk, _.pick no longer works for lodash 4 because _.pickBy was split out.

var foo = {
    alpha: true,
    beta: false,
    gamma: true
};

var t1 = _.keys(_.pickBy(foo, _.identity));
console.log(t1);

var t2 = _(foo).pickBy(_.identity).keys().value();
console.log(t2);

// _.pickBy defaults to _.identity

var t3 = _.keys(_.pickBy(foo));
console.log(t3);

var t4 = _(foo).pickBy().keys().value();
console.log(t4);
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.8.2/lodash.min.js"></script>
<script src="https://getfirebug.com/firebug-lite-debug.js"></script>

Upvotes: 23

AWolf
AWolf

Reputation: 8980

I think you're looking for the pick method.

Return a copy of the object, filtered to only have values for the whitelisted keys (or array of valid keys). Alternatively accepts a predicate indicating which keys to pick. 

var foo = {
    alpha: true,
    beta: false,
    gamma: true
};

var picked = _.pick(foo, function(value) { return value; });
console.log(picked);

$('#output').html(JSON.stringify(picked));
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.5.0/lodash.js"></script>
<div id="output">
</div>

Upvotes: 1

Asmor
Asmor

Reputation: 5181

I found an answer which simultaneously feels kludgy and elegant.

var foo = {
    alpha: true,
    beta: false,
    gamma: true
};
_.invert(foo, true).true

// yields -> ["alpha", "gamma"]

Upvotes: 11

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