2

I need to get a new object countriesFiltered , filtering just countries with population under a billion. I'm using in the map part: return { key : countries[key]}. I think is not correct, how i can build a new object ? i must use push or something like that?

var countries = {
    China: 1371980000,
    India: 1276860000,
    'United States': 321786000,
    Indonesia: 255461700,
    Brazil: 204873000,
    Pakistan: 190860000
};
var countriesFiltered = Object.keys(countries).filter(function(key) {
    return countries[key] <= 1000000000;
}).map(function(key) {
    return { key : countries[key]};
});
console.log(countriesFiltered);
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3
  • hmm, I'm getting an object with the filtered countries after running your code. What are you trying to do? Commented Aug 12, 2016 at 4:05
  • I need like result; var countriesFiltered = { United States': 321786000, Indonesia: 255461700, Brazil: 204873000, Pakistan: 190860000 }; Commented Aug 12, 2016 at 4:09
  • Added an answer and a fiddle. jsfiddle.net/swaprks/aewf0erx Commented Aug 12, 2016 at 4:30

5 Answers 5

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3

Close! Just use Array.reduce instead of Array.map. Object property names can't be computed unless you are using ES2015. So you need to use reduce to construct a new object and then assign each property individually.

var countries = {
  China: 1371980000,
  India: 1276860000,
  'United States': 321786000,
  Indonesia: 255461700,
  Brazil: 204873000,
  Pakistan: 190860000
};
var countriesFiltered = Object.keys(countries).filter(function(key) {
  return countries[key] <= 1000000000;
}).reduce(function(obj, key) {
  // Assign key/val to new object
  obj[key] = countries[key];
  
  return obj;
}, {});

document.write('<pre>' + JSON.stringify(countriesFiltered, null, 2) + '</pre>');

EDIT: Using ES2015 computed name properties would look something like the following. Note this will only work in supported browsers.

var countries = {
  China: 1371980000,
  India: 1276860000,
  'United States': 321786000,
  Indonesia: 255461700,
  Brazil: 204873000,
  Pakistan: 190860000
};
var countriesFiltered = Object.keys(countries).filter(function(key) {
  return countries[key] <= 1000000000;
}).reduce(function(obj, key) {
  // Create object with computed property name
  // and assign to obj
  return Object.assign(obj, {
    [key]: countries[key]
  });
}, {});

document.write('<pre>' + JSON.stringify(countriesFiltered, null, 2) + '</pre>');

Bonus: for fun you could use the replacer function to leverage the power of JSON.stringify to filter the object. While it does show there are a lot of different approaches to solving this I wouldn't recommend this approach. 

var countries = {
  China: 1371980000,
  India: 1276860000,
  'United States': 321786000,
  Indonesia: 255461700,
  Brazil: 204873000,
  Pakistan: 190860000
};
var countriesFiltered = JSON.parse(JSON.stringify(countries, filterCountries));

function filterCountries(key, val) {
  if (val > 1000000000) {
    return undefined;
  }

  return val;
}

document.write('<pre>' + JSON.stringify(countriesFiltered, null, 2) + '</pre>');

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2 Comments

please; can you give me a solution with ES2015 too ? thanks
@stackdave I updated the answer with a computed name property approach as well as a little fun example to maybe broaden your exposure to JavaScript. Enjoy!
0

Try using the following function:

Object.filter = (obj, predicate) => 
    Object.keys(obj)
          .filter(key => predicate(obj[key]))
          .reduce((res, key) => (res[key] = obj[key], res), {});


var filtered = Object.filter(countries, countrie => countrie <= 1000000000); 
console.log(filtered);

This should do it for you!

Reference: JavaScript: filter() for Objects

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4 Comments

I wouldn't recommend modifying the native Object for a variety of reasons.
origina example; just does: return countries[key] <= 1000000000; instead return { key : countries[key]}; in my example... i've thought i needed to change just one line, but I see it's not a simple thing to get an row from the object .... and do a sort of push... i'm studying your solution is very complex for me, but i ll study and i will reply it,
@JasonCust I did not understand very well; the solution is not good then? with Object.filter, is modifying the native object?
@JasonCust - This doesn't affect the filter method itself. It doesn't break any of the current functionality.
0

I am not 100% sure what you are looking for but if you are looking for a new object with each country name as the property and the population you can try.

var countries = {
  China: 1371980000,
  India: 1276860000,
  'United States': 321786000,
  Indonesia: 255461700,
  Brazil: 204873000,
  Pakistan: 190860000
};
var countriesFiltered = {};
Object.keys(countries).filter(function(key) {
  return countries[key] <= 1000000000;
}).map(function(key) {
  countriesFiltered[key] = countries[key];
});
console.log(countriesFiltered);

This results in:

{
    United States: 321786000, 
    Indonesia: 255461700, 
    Brazil: 204873000, 
    Pakistan: 190860000
}

If you want an array of Key Value Pairs you could try.

var countries = {
  China: 1371980000,
  India: 1276860000,
  'United States': 321786000,
  Indonesia: 255461700,
  Brazil: 204873000,
  Pakistan: 190860000
};
var countriesFiltered = Object.keys(countries).filter(function(key) {
  return countries[key] <= 1000000000;
}).map(function(key) {
    return { country: key, population: countries[key]}; 
});
console.log(countriesFiltered);

EDIT: Answer to comment

what does mean exactly, reausable, where i can read about that ?

If you review @answer-38909742 you will see that they have modified the Object type and added a static method Object.filter() with the signature of Object.filter = (obj, predicate) => {}

This then makes it reusable and not limited to the scope of the function but to any object.

If this was placed in a global script somewhere in your application you can then resuse this method on any object in any scope.

As stated in his question simply by calling.

Object.filter(countries, countrie => countrie <= 1000000000);
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7 Comments

This does do it, but it wouldn't really be re-usable as it's pretty much hard coded to use the countries object
i was looking for a solution without use: var countriesFiltered = {}; i need an objet , not an array, i m studying anyway yours solution, thanks
@stackdave if you run the first solution it will return an object, the second solution returns an array.
@James111 agreed it is not reusable. However didnt specify that in the OP. :)
what does mean exactly, reausable, where i can read about that ?
|
0

Object has only unique keys. So if your countries are going to be unique then you can use the following code:

    var countries = {
      China: 1371980000,
      India: 1276860000,
      'United States': 321786000,
      Indonesia: 255461700,
      Brazil: 204873000,
      Pakistan: 190860000
    };
var countriesFiltered = {};

for ( var country in countries ) {
   if ( countries[country] <= 1000000000 ) {
      countriesFiltered[country] = countries[country];
   }
}

console.log(countriesFiltered);
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2 Comments

sorry but i was looking for a solution with .keys and map or something like that
@stackdave check the updated one jsfiddle.net/swaprks/aewf0erx/1
-2

Well I will try to understand your problem instead of giving you a different solution. Actually if you want to assign a variable as a key in a javascript object there is a different way for that. eg.

var obj = {};
var key = 'abc';
obj[key] =  123;

You wont be able to assign a variable as a key directly to an object.

var key = 'abc';
var obj = {key : 123}

It would result in an error.

Here is your answer

 var countries = {
    China: 1371980000,
    India: 1276860000,
    'United States': 321786000,
    Indonesia: 255461700,
    Brazil: 204873000,
    Pakistan: 190860000
};
var countriesFiltered = Object.keys(countries).filter(function(key) {
    return countries[key] <= 1000000000;
}).map(function(key) {
    var obj = {};
    obj[key] = countries[key];
    return obj;
}).reduce(function(prevKey, currentKey) {
    return Object.assign(prevKey , currentKey);
})
    console.log(countriesFiltered);

Follow this good post already posted for the same. JavaScript set object key by variable

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5 Comments

This doesn't actually provide a solution for the OP
Pls explain how this couldn't answer James
Your example returns an object array
You've since change your answer after my initial comment, it still doesn't do what the OP wants. Instead this is returning an Array of objects, not an object with key + values.
Apologies !!! My Bad!! I just added the reduce after map now. In the post StackDave was wrongly interpreted the variable key assignment to an object. just wanted to clear that though.. I guess already it is answered.. Thanks for pointing it out James!! One vote for your comment!

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