Obtain a random item from an array containing elements with assigned weights

Question

Obtain a random item from an array containing elements with assigned weights

In my game development project, I have an array of objects representing creatures. Each creature object includes a unique identifier and a corresponding weight or probability for spawning.

I am struggling to create an algorithm that will randomly spawn creatures based on their weights. I need help figuring out how to implement this feature effectively.

Could anyone provide some guidance?

Here is an example of the creatures array:

var creatures = [
    {id: 1, weight: 25},
    {id: 2, weight: 15},
    {id: 3, weight: 5},
    {id: 4, weight: 45},
    {id: 5, weight: 10}
]

javascript arrays

Answer 1

Answer №1

After coming across a helpful algorithm written in PHP on this blog, I decided to adapt it for use in JavaScript. The algorithm seems like it could be a good fit for your requirements.

Here is the adapted code:

var creatures = [{
    id: 1,
    weight: 25
  }, {
    id: 2,
    weight: 15
  }, {
    id: 3,
    weight: 5
  }, {
    id: 4,
    weight: 45
  }, {
    id: 5,
    weight: 10
  }],
  sumOfWeights = creatures.reduce(function(memo, creature) {
    return memo + creature.weight;
  }, 0),
  selectedWeigths = {};

function getRandom(sumOfWeights) {
  var random = Math.floor(Math.random() * (sumOfWeights + 1));

  return function(creature) {
    random -= creature.weight;
    return random <= 0;
  };
}

for (var i = 0; i < 1000; i++) {
  var creature = creatures.find(getRandom(sumOfWeights));
  selectedWeigths[creature.weight] = (selectedWeigths[creature.weight] || 0) + 1;
}

console.log(selectedWeigths);

I hope this solution proves to be useful for you.

Answer 2

After coming across a helpful algorithm written in PHP on this blog, I decided to adapt it for use in JavaScript. The algorithm seems like it could be a good fit for your requirements.

Here is the adapted code:

var creatures = [{
    id: 1,
    weight: 25
  }, {
    id: 2,
    weight: 15
  }, {
    id: 3,
    weight: 5
  }, {
    id: 4,
    weight: 45
  }, {
    id: 5,
    weight: 10
  }],
  sumOfWeights = creatures.reduce(function(memo, creature) {
    return memo + creature.weight;
  }, 0),
  selectedWeigths = {};

function getRandom(sumOfWeights) {
  var random = Math.floor(Math.random() * (sumOfWeights + 1));

  return function(creature) {
    random -= creature.weight;
    return random <= 0;
  };
}

for (var i = 0; i < 1000; i++) {
  var creature = creatures.find(getRandom(sumOfWeights));
  selectedWeigths[creature.weight] = (selectedWeigths[creature.weight] || 0) + 1;
}

console.log(selectedWeigths);

I hope this solution proves to be useful for you.

Answer 3

Answer №2

To create a new array, iterate through each creature and add its ID to the array based on its weight. Then generate a random number within the range of the array's size to return the corresponding ID.

var creatureIds = [];
for(var i=0;i<creatures.length;i++){
    for(var x=0;x<creatures[i].weight;x++){
        creatureIds.push(creatures[i].id);
    }
}

// Obtain a random index between 0 and the length of IDs.
var min = 0;
var max = creatureIds.length;
var index = Math.floor(Math.random() * (max - min + 1)) + min;

var randomWeightedCreatureId = creatureIds[index];

Answer 4

To create a new array, iterate through each creature and add its ID to the array based on its weight. Then generate a random number within the range of the array's size to return the corresponding ID.

var creatureIds = [];
for(var i=0;i<creatures.length;i++){
    for(var x=0;x<creatures[i].weight;x++){
        creatureIds.push(creatures[i].id);
    }
}

// Obtain a random index between 0 and the length of IDs.
var min = 0;
var max = creatureIds.length;
var index = Math.floor(Math.random() * (max - min + 1)) + min;

var randomWeightedCreatureId = creatureIds[index];

Obtain a random item from an array containing elements with assigned weights

Answer №1

Answer №2

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