how to generate random amount of items from an array

Question

I'm trying to get a random amount of items from an array.

This is what I've got so far:

I'm calling the function (in another part of a long code) with the min and max values:

generateitems(1,7)

And this is the rest:

function generateitems(min, max) {
  var myArray = ["aa","bb","cc","dd","ee","ff","gg"];
  var randomItem = myArray[Math.floor(Math.random()* (max - min)) + min];
  return randomItem;
}

I keep just getting one item as a result. How do I fix this?

I know how to generate one/a specific amount, or all of the items from the array, and my program works when I do that -- so I don't think there's an issue with the rest of my code. I just can't figure out how to use Math.random here, or if it's even the right thing to use in this case.

Thank you for your time.

EDIT:
wanted result:
the function should return 1-7 items
duplicates are ok, I don't care about the order of the items

every item not more than once or are duplicates allowed? random shuffled or in order but random selected? What should happen if max is bigger than the length of the array? I have so many questions... — Niklas E., Mar 15 '20 at 15:36

Terry · Accepted Answer · 2020-03-15T15:45:32.817

That's because on this line in your code, you are generating an array with a single entry:

var randomItem = myArray[Math.floor(Math.random()* (max - min)) + min];

If you want to generate a random number of items, you need to:

Use the min and max value to generate an array of a random length
After the array is generated, you then push a random item into it using Array.prototype.map.

Note that your original logic is flawed: if you want to select a random element from an array. using myArray[Math.floor(Math.random() * myArray.length] should work. The min and max, as I suspect for your case, is only used to determine the length of the randomly generated array.

function generateitems(min, max) {
  var myArray = ["aa","bb","cc","dd","ee","ff","gg"];
  var arrayLength = Math.floor(Math.random()* (max - min)) + min
  
  return [...new Array(arrayLength)].map(function() {
    return myArray[Math.floor(Math.random()* myArray.length)];
  });
}

console.log(generateitems(1,7));

This however, does not generate an array that is unique, because you are basically selecting items from an array at random (which means that is a chance of value collision).

If you want to create a shuffled/randomized subset of an existing array, then this answer will suit your needs the best: Sampling a random subset from an array

score 1 · Answer 2 · answered Mar 15 '20 at 15:45

You need a loop for getting the wanted items and take the length as factor for getting a random index.

function generateitems(min, max) {
  var values = ["aa","bb","cc","dd","ee","ff","gg"],
      result = [],
      items = Math.floor(Math.random() * (max - min)) + min;
      
  while (items--)
      result.push(values[Math.floor(Math.random() * values.length)]);
  
  return result;
}

console.log(generateitems(1, 7));

how to generate random amount of items from an array

2 Answers2