CODEWITHSUNDEEP
javascript
Sjoerd
Sjoerd

Reputation: 191

How to get a hash in an array

I have an array of hashes, how can I get the location of a hash set in the array?

In below example I like to find where on the path a certain location is but it results in a 'not found'

var path = [{x: 42, y: 8}, {x: 42, y: 7}, {x: 42, y: 6}];
var location = {x: 42, y: 6};
var a = path.indexOf(location); // this result is -1

Upvotes: 2

Views: 120

Answers (3)

Ram
Ram

Reputation: 144729

That's because the location object and the corresponding object in the array point to different locations in memory and are not considered equal by JavaScript interpreter, i.e even {} === {} results in false as these are 2 unique objects, but:

var a = {}, b = a;

if (a === b) // true

Note that is not the case for primitive values like numbers.

For filtering the corresponding object you should iterate through the array and compare each element's x and y properties against the x and y properties of the location object, something like:

var index = -1;
var matched = path.filter(function(el, i) {
    var matched = location.x === el.x && location.y === el.y;
    if (matched) index = i;
    return matched;
}); // [0]

Upvotes: 3

elpddev
elpddev

Reputation: 4494

Just to add to the solutions options, you can use Lodash, or a custom array find function to iterate on the set and find the object you want.

Using Array.prototype.findIndex or It's polyfill

function Point(x, y) {
  this.x = x;
  this.y = y;
} 

Point.prototype = {
  equal: function(point) { 
    if (point.x == this.x && point.y == this.y) {
      return true; 
    } 

    return false;
  }
}

point1 = new Point(6,1);

console.log([ 
  new Point(4,0), 
  new Point(6,1), 
  new Point(8,12)].findIndex(
    function(element, index, array){
      return element.equal(point1);
    })); 

>> 1

Using Lodash findIndex

var users = [
  { 'user': 'barney',  'age': 36, 'active': true },
  { 'user': 'fred',    'age': 40, 'active': false },
  { 'user': 'pebbles', 'age': 1,  'active': true }
];

// using the `_.matches` callback shorthand
_.findIndex(users, { 'user': 'fred', 'active': false });
// → 1

Upvotes: 1

Mallen
Mallen

Reputation: 262

It depends what exactly you want. If you want to compare against a specific object you are already doing it right. For example:

var foo = { x: 1, y: 3 };
var not_foo = { x: 1, y: 3 };
var arrayOfThings = [foo, { x:3, y:4 }];

// this will work because foo is in there
var index = arrayOfThings.indexOf(foo);

// this will not work because not_foo is not in there
var fails = arrayOfThings.indexOf(not_foo);

If you want to find a identical object you have to get tricky. You could use a library, such as underscore which has both a filter, and find method which could be applicable. You could also use something like:

var foo = { x: 1, y: 3 };
var not_foo = { x: 1, y: 3 };
var arrayOfThings = [foo, { x:3, y:4 }];

arrayOfThings.forEach(function(obj){
    if (obj.x == foo.x && obj.y == foo.y) {
    // we found a match so do something I guess!
    }
});

Upvotes: 0

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