Finding the index of an object within an array efficiently

Question

I am trying to find the index of an object within an array. I know there is a way to do this with underscore.js but I am trying to find an efficient way without underscore.js. Here is what I have :

var arrayOfObjs = [{
  "ob1": "test1"
}, {
  "ob2": "test1"
}, {
  "ob1": "test3"
}];

function FindIndex(key) {
  var rx = /\{.*?\}/;            // regex: finds string that starts with { and ends with }
  var arr = [];                  // creates new array
  var str = JSON.stringify(arrayOfObjs);          // turns array of objects into a string
  for (i = 0; i < arrayOfObjs.length; i++) {      // loops through array of objects
    arr.push(str.match(rx)[0]);                   // pushes matched string into new array
    str = str.replace(rx, '');                    // removes matched string from str
  }
  var Index = arr.indexOf(JSON.stringify(key));   // stringfy key and finds index of key in the new array
  alert(Index);
}

FindIndex({"ob2": "test1"});

JSFIDDLE

This works but I am afraid it isn't very efficient. Any alternatives?

Answer 1

Here's one way to do it, somewhat reliably and a little more efficiently, using some() and stopping as soon as the objects don't match etc.

var arrayOfObjs = [{
  "ob1": "test1"
}, {
  "ob2": "test1"
}, {
  "ob1": "test3"
}];

function FindIndex(key) {
    var index = -1;

    arrayOfObjs.some(function(item, i) {
    	var result = Object.keys(key).some(function(oKey) {
            return (oKey in item && item[oKey] === key[oKey]);
        });
        if (result) index = i;
        return result;
    });
    
    return index;
}

var index = FindIndex({"ob2": "test1"});

document.body.innerHTML = "'{\"ob2\": \"test1\"}' is at index : " + index;

Answer 2

A hash table with an example of access.

var arrayOfObjs = [{ "obj1": "test1" }, { "obj2": "test1" }, { "obj1": "test3" }],
    hash = {};

arrayOfObjs.forEach(function (a, i) {
    Object.keys(a).forEach(function (k) {
        hash[k] = hash[k] || {};
        hash[k][a[k]] = i;
    });
});

document.write('<pre>' + JSON.stringify(hash['obj2']['test1'], 0, 4) + '</pre>');
document.write('<pre>' + JSON.stringify(hash, 0, 4) + '</pre>');