Pick random property from a Javascript object
JavascriptRandomJavascript Problem Overview
Suppose you have a Javascript object like {'cat':'meow','dog':'woof' ...} Is there a more concise way to pick a random property from the object than this long winded way I came up with:
function pickRandomProperty(obj) {
var prop, len = 0, randomPos, pos = 0;
for (prop in obj) {
if (obj.hasOwnProperty(prop)) {
len += 1;
}
}
randomPos = Math.floor(Math.random() * len);
for (prop in obj) {
if (obj.hasOwnProperty(prop)) {
if (pos === randomPos) {
return prop;
}
pos += 1;
}
}
}
Javascript Solutions
Solution 1 - Javascript
The chosen answer will work well. However, this answer will run faster:
var randomProperty = function (obj) {
var keys = Object.keys(obj);
return obj[keys[ keys.length * Math.random() << 0]];
};
Solution 2 - Javascript
http://geomblog.blogspot.com/2008/01/happy-birthday-don-knuth.html">Picking a random element from a stream
function pickRandomProperty(obj) {
var result;
var count = 0;
for (var prop in obj)
if (Math.random() < 1/++count)
result = prop;
return result;
}
Solution 3 - Javascript
I didn't think any of the examples were confusing enough, so here's a really hard to read example doing the same thing.
Edit: You probably shouldn't do this unless you want your coworkers to hate you.
var animals = {
'cat': 'meow',
'dog': 'woof',
'cow': 'moo',
'sheep': 'baaah',
'bird': 'tweet'
};
// Random Key
console.log(Object.keys(animals)[Math.floor(Math.random()*Object.keys(animals).length)]);
// Random Value
console.log(animals[Object.keys(animals)[Math.floor(Math.random()*Object.keys(animals).length)]]);
Explanation:
// gets an array of keys in the animals object.
Object.keys(animals)
// This is a number between 0 and the length of the number of keys in the animals object
Math.floor(Math.random()*Object.keys(animals).length)
// Thus this will return a random key
// Object.keys(animals)[0], Object.keys(animals)[1], etc
Object.keys(animals)[Math.floor(Math.random()*Object.keys(animals).length)]
// Then of course you can use the random key to get a random value
// animals['cat'], animals['dog'], animals['cow'], etc
animals[Object.keys(animals)[Math.floor(Math.random()*Object.keys(animals).length)]]
Long hand, less confusing:
var animalArray = Object.keys(animals);
var randomNumber = Math.random();
var animalIndex = Math.floor(randomNumber * animalArray.length);
var randomKey = animalArray[animalIndex];
// This will course this will return the value of the randomKey
// instead of a fresh random value
var randomValue = animals[randomKey];
Solution 4 - Javascript
If you are capable of using libraries, you may find that Lo-Dash JS library has lots of very useful methods for such cases. In this case, go ahead and check _.sample()
.
(Note Lo-Dash convention is naming the library object _. Don't forget to check installation in the same page to set it up for your project.)
_.sample([1, 2, 3, 4]);
// → 2
In your case, go ahead and use:
_.sample({
cat: 'meow',
dog: 'woof',
mouse: 'squeak'
});
// → "woof"
Solution 5 - Javascript
You can just build an array of keys while walking through the object.
var keys = [];
for (var prop in obj) {
if (obj.hasOwnProperty(prop)) {
keys.push(prop);
}
}
Then, randomly pick an element from the keys:
return keys[keys.length * Math.random() << 0];
Solution 6 - Javascript
If you're using underscore.js you can do:
_.sample(Object.keys(animals));
Extra:
If you need multiple random properties add a number:
_.sample(Object.keys(animals), 3);
If you need a new object with only those random properties:
const props = _.sample(Object.keys(animals), 3);
const newObject = _.pick(animals, (val, key) => props.indexOf(key) > -1);
Solution 7 - Javascript
You can use the following code to pick a random property from a JavaScript object:
function randomobj(obj) {
var objkeys = Object.keys(obj)
return objkeys[Math.floor(Math.random() * objkeys.length)]
}
var example = {foo:"bar",hi:"hello"}
var randomval = example[randomobj(example)] // will return to value
// do something
Solution 8 - Javascript
Another simple way to do this would be defining a function that applies Math.random()
function.
This function returns a random integer that ranges from the 'min'
function getRandomArbitrary(min, max) {
return Math.floor(Math.random() * (max - min) + min);
}
Then, extract either a 'key' or a 'value' or 'both' from your Javascript object each time you supply the above function as a parameter.
var randNum = getRandomArbitrary(0, 7);
var index = randNum;
return Object.key(index); // Returns a random key
return Object.values(index); //Returns the corresponding value.
Solution 9 - Javascript
A lot of great answers here, so let me just try to spread the awareness of the bitwise NOT (~) operator in its double-trouble variant (which I'm pretty sure I learned about on StackOverflow, anways).
Typically, you'd pick a random number from one to ten like this:
Math.floor(Math.random()*10) + 1
But bitwise operation means rounding gets done faster, so the following implementation has the potential to be noticeably more performant, assuming you're doing enough truckloads of these operations:
~~(Math.random()*10) + 1