Add Array item to Array X times

Question

I have a base array of 6 different words that represent game elements. Just wondering how I would multiply the number of instances of each word within the array.

var gameItem = [cattle, wood, stone, metal, grain, craft];

That is, say I want 10 instances of each word to be added to the array, how would I do that? Order isn't important as it'll be shuffled.

• StarPinkER: why not a loop?
• C_K: @JermaineXu ; I was hoping for something that isn't performance intensive.
• Felix Kling: Worry about performance when you have a performance problem.
• Robin van Baalen: @FelixKling you don't have performance problems when you 'worry about performance' by design ;-) But you sure have a good point here. That being said, it's not forbidden to use loops; even in performance critical situations. Sometimes it's just the right way.
• jfriend00: @RobinvanBaalen - I disagree. You don't have performance problems when you use smart design and then you save your optimization time for actual performance problems in your working app and then you measure carefully to understand where you can make a difference. Premature optimization is wasted time and usually targeted at the wrong thing which just makes your code take longer to write, more complicated to get right and larger without actually being focused in the right areas.

Answer 1

Don't forget that your array doesn't work unless you define each of those variable. But as I understand, those are words, not vars. So the right array declaration is:

var newGameItem = ["cattle", "wood", "stone", "metal", "grain", "craft"]

To repeat that array 10 times, you can use a for loop and the array method concat().

var newGameItem = [];
for(var i=0 ; i<10 ; i++) {
 newGameItem = newGameItem.concat(gameItem);
}
> newGameItem : ["cattle", "wood", "stone", "metal", "grain", "craft", "cattle" ... ]

I don't know what is your idea for this, but, if you want to store a quantity of elements of those kinds, like, player has 1 cattle, 12 wood, 20 stone, etc ... You probably should have a better data structure, like this:

 var gameItem = {"cattle" : 1, "wood" : 12, "stone" : 20, "metal" : 0, "grain" : 0, "craft" : 0 };

So by doing gameItem.wood, you get the result > 12

• C_K: Gave you the answer because of the {"w" : 1} part. To everyone else, thanks, I went with looping and .push, no real performance issues.

Answer 2

You just need a couple loops:

function dupElements(arr, n) {
 for (var i = 0, len = arr.length; i < len; i++) {
 for (var j = 0; j < n; j++) {
 arr.push(arr[i]);
 }
 }
}
dupElements(gameItem, 10);

The outer loop cycles through the initial elements. The inner loop adds n copies of each.

Answer 3

You can do:

var gameItem = ['cattle', 'wood', 'stone', 'metal', 'grain', 'craft'];
var doublearr = gameItem.concat(gameItem); //x2
gameItem = doublearr.concat(doublearr);//x4
gameItem = gameItem.concat(gameItem );//x8
gameItem = gameItem.concat(doublearr);//x10 
alert(gameItem); 

Concatenate the array to itself until you reach the closest ^2 (below - in our case 8 = 2^3) and then add the rest.

I posted this solution because you wrote in one of the comments that you hope for something that isn't performance intensive. But I agree with the others that it's more readable and easier to maintain a simple for-loop. So if you have only x10 - keep it simple.