Pick values of given properties from object into array

Question

I have an object:

person = { 
    birth_year: 1970, 
    first_name: "John", 
    last_name: "Doe", 
    occupation: "Doctor", 
    city: "Boston",
    married: true 
}

I have an array of key names in given order:

keys = ["occupation", "last_name", "city"]

I want to get this array:

["Doctor", "Doe", "Boston"]

It is important, that the answer should guarantee the order (JavaScript does not guarantee the order for object iteration).

I think there is probably some utility function in lodash/underscore to do it simply, but can't figure out any.

user3297291 · Accepted Answer · 2016-11-09T12:17:29.397

You can use Array.prototype.map for this. Map loops through an array and creates a new array by applying a function to each item. When you use the keys array as a starting point, and return the value in o for that key, you'll get a new array with only values.

When using "dynamic" key names, you use a object[stringKeyName] notation to retrieve a value.

var o = { 
    birth_year: 1970, 
    first_name: "John", 
    last_name: "Doe", 
    occupation: "Doctor", 
    city: "Boston",
    married: true 
};

var keys = ["occupation", "last_name", "city"];

var result = keys.map(function(k) { return o[k]; });

console.log(result);

If it fits your style, you can create a helper method to replace the anonymous function:

var o = { birth_year: 1970, first_name: "John", last_name: "Doe", occupation: "Doctor", city: "Boston", married: true };
var keys = ["occupation", "last_name", "city"];

var prop = obj => key => obj[key];
var result = keys.map(prop(o));

console.log(result);

We could even simplify this into `var result = keys.map(k => o[k])`, but I still don't like it. — Mikhail Batcer, Nov 09 '16 at 12:12
If it's a matter of style, you could wrap some stuff in a helper. Have a look at the second snippet. — user3297291, Nov 09 '16 at 12:18
If the order matters, this or the `_.map` function is the way to go. — Emile Bergeron, Nov 09 '16 at 16:28

score 4 · Answer 2 · answered Nov 09 '16 at 12:15

4

With Lodash you could use pick and values

var o = {
  birth_year: 1970,
  first_name: "John",
  last_name: "Doe",
  occupation: "Doctor",
  city: "Boston",
  married: true
}
var keys = ["occupation", "last_name", "city"];

var result = _.values(_.pick(o, keys));
console.log(result)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script>

answered Nov 09 '16 at 12:15

Nenad Vracar

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Does it guarantee the order? – Mikhail Batcer Nov 09 '16 at 12:19
@Mikhail Batcer I am not sure about that. – Nenad Vracar Nov 09 '16 at 12:21
@NenadVracar That's the reason I asked this "nooby" question... :)) – Mikhail Batcer Nov 09 '16 at 12:23
1

`pick` creates an object, `values` loops through an object's keys. Object keys are not sorted by spec (http://stackoverflow.com/a/5525820/3297291), so you can't expect `result` to follow the order of `keys` in this example. – user3297291 Nov 09 '16 at 12:46

Pick values of given properties from object into array

2 Answers2