Create array of keys by sorting values

Question

I have an object that looks like this

myList: {  
id1:{  
      ts:'2010-01-12T00:51:00',
      name:"roger"
     },  
id2:{  
      ts:'2011-01-12T05:22:00',
      name: "Tom"
  },  
id3:{  
      ts:'2013-01-12T11:32:00',
      name:"Jack"
  }
}

I know objects cant be sorted so i wanted to know how i can generate an array of just the keys,which are sorted according to the key "ts". I want this in descending order.

So the array for the above object will be [id3,id2,id1]

once i have this array i can make operations like this where arr is sorted array and myList is the object

for(var i=0:i<arr.length;i++)
{
alert(myList[arr[i]].name);
}

As written, the ts values above are 1997, 1998 and 2000, but it seems doubtful that this is what's intended. — Semicolon
– Semicolon, Commented Jan 20, 2014 at 7:16
I am new to js so if you have a soln where i can generate such an array i would appreciate it — vijar
– vijar, Commented Jan 20, 2014 at 7:17
You may want to read stackoverflow.com/questions/2947822/javascript-sort-objects Also, string should have quotes around them or else it's just math at best. — user1932079
– user1932079, Commented Jan 20, 2014 at 7:20
You basically want a collection: list=[{id:1,ts:'2010-01-12'},{id:2,ts:'2011-01-12'},...] — elclanrs
– elclanrs, Commented Jan 20, 2014 at 7:22

zerkms · Accepted Answer · 2014-01-20 07:33:25Z

1

var keys = Object.keys(myList).sort(function(a, b) {
    if (myList[a].ts == myList[b].ts) {
        return 0;
    }
    return myList[a].ts < myList[b].ts ? 1 : -1;
});

console.log(keys);

jsfiddle: http://jsfiddle.net/pWq2L/

Explanation:

First you export keys from the object: Object.keys(myList)
You sort using custom comparison function and in it you refer to the .ts attribute of the compared values. a and b are the keys of the compared elements

References:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

answered Jan 20, 2014 at 7:33

zerkms

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Comments

Semicolon · Accepted Answer · 2014-01-20 07:34:12Z

0

Given this data structure, and assuming there is a good reason for it to not be an array:

var myList = {
  id1: {  
    ts: new Date('2010-01-12T00:51:00'),
    name: 'Roger'
  },
  id2: {  
    ts: new Date('2011-01-12T05:22:00'),
    name: 'Tom'
  },  
  id3:{  
    ts: new Date('2013-01-12T11:32:00'),
    name: 'Jack'
  }
}

We can create and sort an array like so:

var arr = [];
Object.keys(myList).forEach(function(item) {
  arr.push(myList[item]);
});
arr.sort(function(a, b) {
  return a.ts > b.ts ? -1 : a.ts < b.ts ? 1 : 0;
})

answered Jan 20, 2014 at 7:34

Semicolon

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Comments

roland · Accepted Answer · 2014-01-20 09:02:11Z

0

One way to extend zerkms solution is to work with an object augmented with smart properties. The versatile reduce comes in handy:

var result = keys.reduce(function(arr, k, i) {
    var item = {
      key: k,
      index: i,
      value: myList[k]
    };
    arr.push(item);
    return arr;
}, []);


//result:
[
  { index:0 , key: id3, value: {...} },
  { index:1 , key: id2, value: {...} },
  { index:2 , key: id1, value: {...} }
]

reduce is part of the ECMAScript 5th edition; so you may fill in some gap with a polyfill.

http://jsfiddle.net/pWq2L/3/

answered Jan 20, 2014 at 9:02

roland

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