Get object keys for filtered values

Question

The case is simple - I\'ve got a following object:

Object {1: false, 2: true, 3: false, 4: false, 5: false, 6: false, 7: false, 8: true, 12: false, 13: false, 14         


        

Answer 1

I Do not know underscore.js. But using normal JS, I have written the below code.

function myFunction()
{
var str="1: false; 2: true; 3: false; 4: false; 5: false; 6: false; 7: false; 9: true; 12: false";
var n=str.split(";");

for(var i=0;i<n.length;i++)
{
     if(n[i].search("true")!=-1){
     alert(n[i].slice(0,n[i].search(":")));
     }
}

Answer 2

My version:

var list = {
    1: false, 2: true, 3: false, 4: false,
    5: false, 6: false, 7: false, 8: true,
    12: false, 13: false, 14: false, 15: false,
    16: false, 17: false, 18: false, 19: false
};

_.chain(list).map(function(val, key) {
    return val ? parseInt(key) : undefined
}).reject(function(val) {
    return _.isUndefined(val);
}).value();
// returns [2,8]

Answer 3

This might be easier

result = _.chain(obj)
    .map(function(value, key){
        return value?key:false;
    })
    .filter(function(v){
        return v
    })
    .value();

Answer 4

You can try this:

_.pairs(obj)
 .filter(function(pair) { return pair[1] })
 .map(function(pair) { return pair[0] })

Or the same but bit more concise:

_.pairs(obj).filter(_.last).map(_.first)

Answer 5

Another potential solution:

// Your example data
var data = {1: false, 2: true, 3: false, 4: false, 5: false, 6: false, 7: false, 8: true, 12: false, 13: false, 14: false, 15: false, 16: false, 17: false, 18: false, 19: false};

// Outputs the keys: ["2", "8"]
_.keys(_.transform(data, function(r, v, k) { v ? r[k] = 1 : null; }));

// Outputs the keys as integers: [2, 8]
_.map(_.keys(_.transform(data, function(r, v, k) { v ? r[k] = 1 : null; })), _.parseInt)

So basically:

1. Transform the original object to strip out the false-valued keys
2. Grab the list of keys from the transformed result
3. Convert the keys to ints if you need to

Answer 6

I use this one: Retrieve all keys with the same value from an object (not only an object with just boolean values) using lodash

function allKeys(obj, value) {
  _.keys(_.pick(obj, function (v, k) { return v === value; }));
}

Example:

var o = {a: 3, b: 5, c: 3};
var desiredKeys = allKeys(o, 3);
// => [a, c]