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Mini Shell
Mini Shell
'use strict'
// Hacked https://github.com/felixge/node-measured
var BinaryHeap = require('./BinaryHeap')
var units = require('./units')
module.exports = ExponentiallyDecayingSample
function ExponentiallyDecayingSample (options) {
options = options || {}
this._elements = new BinaryHeap({
score: function (element) {
return -element.priority
}
})
this._rescaleInterval = options.rescaleInterval || ExponentiallyDecayingSample.RESCALE_INTERVAL
this._alpha = options.alpha || ExponentiallyDecayingSample.ALPHA
this._size = options.size || ExponentiallyDecayingSample.SIZE
this._random = options.random || this._random
this._landmark = null
this._nextRescale = null
this._mean = null
}
ExponentiallyDecayingSample.RESCALE_INTERVAL = 1 * units.HOURS
ExponentiallyDecayingSample.ALPHA = 0.015
ExponentiallyDecayingSample.SIZE = 1028
ExponentiallyDecayingSample.prototype.update = function (value, timestamp) {
var now = Date.now()
if (!this._landmark) {
this._landmark = now
this._nextRescale = this._landmark + this._rescaleInterval
}
timestamp = timestamp || now
var newSize = this._elements.size() + 1
var element = {
priority: this._priority(timestamp - this._landmark),
value: value
}
if (newSize <= this._size) {
this._elements.add(element)
} else if (element.priority > this._elements.first().priority) {
this._elements.removeFirst()
this._elements.add(element)
}
if (now >= this._nextRescale) this._rescale(now)
}
ExponentiallyDecayingSample.prototype.toSortedArray = function () {
return this._elements
.toSortedArray()
.map(function (element) {
return element.value
})
}
ExponentiallyDecayingSample.prototype.toArray = function () {
return this._elements
.toArray()
.map(function (element) {
return element.value
})
}
ExponentiallyDecayingSample.prototype._weight = function (age) {
// We divide by 1000 to not run into huge numbers before reaching a
// rescale event.
return Math.exp(this._alpha * (age / 1000))
}
ExponentiallyDecayingSample.prototype._priority = function (age) {
return this._weight(age) / this._random()
}
ExponentiallyDecayingSample.prototype._random = function () {
return Math.random()
}
ExponentiallyDecayingSample.prototype._rescale = function (now) {
now = now || Date.now()
var self = this
var oldLandmark = this._landmark
this._landmark = now || Date.now()
this._nextRescale = now + this._rescaleInterval
var factor = self._priority(-(self._landmark - oldLandmark))
this._elements
.toArray()
.forEach(function (element) {
element.priority *= factor
})
}
ExponentiallyDecayingSample.prototype.avg = function (now) {
var sum = 0
this._elements
.toArray()
.forEach(function (element) {
sum += element.value
})
return (sum / this._elements.size())
}
Zerion Mini Shell 1.0