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/**
* Returns a random integer between min (inclusive) and max (inclusive).
* The value is no lower than min (or the next integer greater than min
* if min isn't an integer) and no greater than max (or the next integer
* lower than max if max isn't an integer).
* Using Math.round() will give you a non-uniform distribution!
* https://stackoverflow.com/questions/1527803/generating-random-whole-numbers-in-javascript-in-a-specific-range
*/
const getRandomInt = (min, max) => {
min = Math.ceil(min)
max = Math.floor(max)
return Math.floor(Math.random() * (max - min + 1)) + min
}
/**
* Reply Buffer.
*/
class ReplyBuffer {
/**
* Constructor.
*
* @param {*} limit maximum number of transitions
* @param {*} onDiscard callback triggered on discard a transition
*/
constructor(limit = 500, onDiscard = () => {}) {
this._limit = limit
this._onDiscard = onDiscard
this._buffer = new Array(limit).fill()
this._pool = []
this.size = 0
}
/**
* Add a new transition to the reply buffer.
* Transition doesn't contain the next state. The next state is derived when sampling.
*
* @param {{id: number, priority: number, state: array, action, reward: number}} transition transition
*/
add(transition) {
let { id, priority = 1 } = transition
if (id === undefined || id < 0 || priority < 1)
throw new Error('Invalid arguments')
id = id % this._limit
if (this._buffer[id]) {
const start = this._pool.indexOf(id)
let deleteCount = 0
while (this._pool[start + deleteCount] == id)
deleteCount++
this._pool.splice(start, deleteCount)
this._onDiscard(this._buffer[id])
} else
this.size++
while (priority--)
this._pool.push(id)
this._buffer[id] = transition
}
/**
* Return `n` random samples from the buffer.
* Returns an empty array if impossible provide required number of samples.
*
* @param {number} [n = 1] - number of samples
* @returns array of exactly `n` samples
*/
sample(n = 1) {
if (this.size < n)
return []
const
sampleIndices = new Set(),
samples = []
let counter = n
while (counter--)
while (sampleIndices.size < this.size) {
const randomIndex = this._pool[getRandomInt(0, this._pool.length - 1)]
if (sampleIndices.has(randomIndex))
continue
sampleIndices.add(randomIndex)
const { id, state, action, reward } = this._buffer[randomIndex]
const nextId = id + 1
const next = this._buffer[nextId % this._limit]
if (next && next.id === nextId) { // the case when sampled the last element that still waiting for next state
samples.push({ state, action, reward, nextState: next.state})
break
}
}
return samples.length == n ? samples : []
}
}
/** TESTS */
(() => {
return
const rb = new ReplyBuffer(5)
rb.add({id: 0, state: 0})
rb.add({id: 1, state: 1})
rb.add({id: 2, state: 2, priority: 3})
console.assert(rb.size === 3)
console.assert(rb._pool.length === 5)
console.assert(rb._buffer[0].id === 0)
rb.add({id: 2, state: 2})
rb.add({id: 4, state: 4, priority: 2})
console.assert(rb.size === 4)
console.assert(rb._pool.length === 5)
console.assert(JSON.stringify(rb._pool) === '[0,1,2,4,4]')
rb.add({id: 5, state: 0, priority: 2}) // 5%5 = 0 => state = 0
console.assert(rb.size === 4)
console.assert(rb._pool.length === 6)
console.assert(rb._buffer.length === 5)
console.assert(rb._buffer[0].id === 5)
console.assert(JSON.stringify(rb._pool) === '[1,2,4,4,0,0]')
console.assert(rb.sample(999).length === 0, 'Too many samples')
let samples1 = rb.sample(2)
console.assert(samples1.length === 2, 'Only two samples possible')
console.assert(samples1[0].nextState === (samples1[0].state + 1) % 5, 'Next state should be valid', samples1)
rb.add({id: 506, state: 506, priority: 3})
let samples2 = rb.sample(1)
console.assert(samples2.length === 1, 'Only one suitable sample with valid next state')
console.assert(samples2[0].state === 4, 'Sample with id:4')
console.assert(rb._buffer[1].id === 506, '506 % 5 = 1')
console.assert(rb.sample(2).length === 0,
'Can not sample 2 transitions since next state is available only for one state')
})()
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