javascript associative array access by key value

Question

I have an array like this:

employees = [
        {
        "id": 1,
        "shift_id": 1,
        "days": {
            "2012-03-01": 1,
            "2012-03-02": 1,
            "2012-03-03": 1,
            "2012-03-04": 0,
            "2012-03-05": 0,
            "2012-03-06": 0
        }},
    {
        "id": 2,
        "shift_id": 1,
        "days": {
            "2012-03-01": 0,
            "2012-03-02": 1,
            "2012-03-03": 1,
            "2012-03-04": 1,
            "2012-03-05": 1,
            "2012-03-06": 0
        }},
    {
        "id": 3,
        "shift_id": 2,
        "days": {
            "2012-03-01": 0,
            "2012-03-02": 0,
            "2012-03-03": 1,
            "2012-03-04": 1,
            "2012-03-05": 1,
            "2012-03-06": 1
        }}

    ];

is there a way to access an element in this array using the id value? maybe something in jquery? like $(employees('id = 1');

could you not just use ID's as numerical indexes for the array? — Mild Fuzz
– Mild Fuzz, Commented Oct 15, 2012 at 8:08
That would be easiest, but I have given a detailed answer of how you could do it with some sexy prototypical inheritance. — Mild Fuzz
– Mild Fuzz, Commented Oct 15, 2012 at 8:23
possible duplicate of javascript find value from array based on associative array key value — qodeninja
– qodeninja, Commented Oct 19, 2014 at 19:32

dan-lee · Accepted Answer · 2012-10-15 08:09:58Z

8

Just loop through your array and check for the id:

var yourId = 1;
for (var i = 0, len = employees.length; i < len; i++) {
  if (employees[i].id == yourId) {
     // ...
  }
}

answered Oct 15, 2012 at 8:09

dan-lee

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Comments

Xophmeister · Accepted Answer · 2012-10-15 08:15:53Z

4

You can use a function like this, which filters the array appropriately:

var getEmployee = function (id) {
  return employees.filter(function(i) { return i.id == id; });
};

answered Oct 15, 2012 at 8:15

Xophmeister

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1 Comment

Xophmeister Over a year ago

n.b. Array.prototype.filter doesn't have full browser support, but you can always roll your own

Michal Klouda · Accepted Answer · 2012-10-15 08:17:31Z

4

You can use .grep() method documented here:

var employee = $.grep(employees, function(e) { return e.id == 1 })[0];

answered Oct 15, 2012 at 8:17

Michal Klouda

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Comments

raina77ow · Accepted Answer · 2012-10-15 08:14:02Z

3

Well, there's a jQuery way of doing it:

var findElementById = function(elements, id) {
  return $.grep(elements, function(e) { return e.id === id; })[0];
}

Still I wonder why don't you just index the source array by id instead.

answered Oct 15, 2012 at 8:14

raina77ow

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Comments

dangel · Accepted Answer · 2012-10-15 08:15:43Z

2

Maybe you are looking for something like the below:

$.grep(employees, function(n){return n.id==1});

answered Oct 15, 2012 at 8:15

dangel

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Comments

nix · Accepted Answer · 2012-10-15 08:27:50Z

2

Or this:

$.each(employee, function(){
    if(this["id"] == 2){
        console.log(this);
    }
});

edited Oct 15, 2012 at 8:27

answered Oct 15, 2012 at 8:08

nix

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1 Comment

Mild Fuzz Over a year ago

But that isn't the OP wants. They need to access the whole object.

Mild Fuzz · Accepted Answer · 2014-10-19 20:35:34Z

1

As far as I am aware, in order to achieve that you would have to loop through them

 Array.prototype.getObjectById = function(x){
      var catcher = false, i = 0;
      while(!catcher){
        catcher = this[i].id == x ? this[i] : false;
        i++;
      }
      return catcher;
    }

This function should help. It will extend the array object so you can use it as myArray.getObjectbyId(id);

By design, this will return the first object that meets the criteria. You could extend it like so:

Array.prototype.getObjectsById = function(x){
  var catcher = [], i = 0;
  for(var i = 0; i < this.length; i++){
    if(this[i].id == value){
      catcher.push(this[i]);
    }
    i++;
  }
  return catcher.length == 1 ? catcher[0] : catcher;
}

This will return an array of objects if more than one object matches the criteria.

 Array.prototype.getObjectsByAttribute = function(x, criteria){
      if(!criteria){criteria = 'id';}
      var catcher = [], i = 0;
      for(var i = 0; i < this.length; i++){
        if(this[i].criteria == value){
         catcher.push(this[i]);
        }
        i++;
      }
      return catcher.length == 1 ? catcher[0] : catcher;
    }

This extends it further to look for any criteria.

edited Oct 19, 2014 at 20:35

answered Oct 15, 2012 at 8:12

Mild Fuzz

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5 Comments

Aladdin Mhemed Over a year ago

please take a look at this: fiddle.jshell.net/AladdinMhaimeed/45cne/14 it gives an error: "Uncaught SyntaxError: Unexpected token catch"

Aladdin Mhemed Over a year ago

I changed the name of the variable catch to catch1, and now no error :)

Mild Fuzz Over a year ago

yeah, it's a reserved word. I've edited my answer to change it.

qodeninja Over a year ago

I'm sure you've heard this a million times by now, but extending native objects is generally a no-no due to performance issues and bugs it can easily introduce.

Mild Fuzz Over a year ago

It can introduce bugs if poorly used, or used in an environment where multiple developers are working, or likely to work. If the code is well documented and sensible naming conventions are used, the risk is minimal. I am not convinced there would ever be performance issues of real concern. It's a valid tool and should be part of your toolkit for appropriate use. This is an appropriate use for me.

qodeninja · Accepted Answer · 2014-10-19 19:15:37Z

I know this question is old, but for future reference if anyone else stumbles upon this question ...

Instead of trying to over-engineer a function to parse/examine your JSON, consider changing the structure of your data to suit its purpose.

Consider the example in the question:

 data =  [ {
    "id": 1,
    "shift_id": 1,
    "days": {
        "2012-03-01": 1,
        "2012-03-02": 1,
        "2012-03-03": 1,
        "2012-03-04": 0,
        "2012-03-05": 0,
        "2012-03-06": 0
    }}, { .. }, {...} ]

Structuring the data in this way only gives you sequential access to the objects with no way to lookup an object by a particular index. Array indices are generally meaningless in this context.

data[0] => { id : 1, .. }
data[1] => { id : 2, .. }

What happens if the id is non-sequential or alphanumeric?

Using an array wont help you search any faster, you'll still have to loop...

Instead consider using a hash table/object:

{
'id1' =>  { id : 1 , data : { ... } }, 
'id99' => { id : 99, data : { ... } },
'id2' =>  { id : 2 , data : { ... } },
}

You can use a string value for the key and get direct access to the data by doing something like:

 data['id2'] => { id : 2, ... }

Which will give you direct access to the data you want to find (by id). By simply re-organizing the structure of the data we were able to go from a O(n) search to an O(1) search.

Keep in mind that this method may work better for some solutions than others, and there are a number of other considerations to make.

This is just one approach to how you might solve a problem when you want to lookup data by a unique property.

reading this before i decided on a data structure helped me a lot, thanks.. Always worth a little bit of planning before diving in :-)

Larry R. Irwin · Accepted Answer · 2022-10-26 19:05:45Z

0

The accepted answer is great - modified a bit for an AngularJS app:

  $rootScope.getObjectsByAttribute = function(inarry,infldnm,infldval){
    // This will iterate through a fetchAll sql result set and return rows where fldnm==fldval
    // If it finds 1 row it returns a single object, if more than that it returns an array of objects
    // Usage: result = $rootScope.getObjectsByAttribute(myarray,'myfldnm',myfldval);
    if(!infldnm){infldnm = 'id';}
    var catcher = [], i = 0;
    for(i = 0; i < inarry.length; i++){
      if(inarry[i][infldnm] == infldval){
        catcher.push(inarry[i]);
      }
    }
    return catcher.length == 1 ? catcher[0] : catcher;
  }

answered Oct 26, 2022 at 19:05

Larry R. Irwin

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