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    pull-window

Aggregate a pull-stream into windows.


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pull-window

Aggregate a pull-stream into windows.

Several helpers are provided for particular types of windows, sliding, tumbling, etc.

And also, a low level

Example: "tumbling" window

sum every 10 items.

var pull   = require('pull-stream')
var window = require('pull-window')

function everyTen () {
  var i = 0
  //window calls init with each data item,
  //and a callback to close that window.
  return window(function (data, cb) {
    //if you don't want to start a window here,
    //return undefined
    if(i != 0) return
    var sum = 0

    //else return a function.
    //this will be called all data
    //until you callback.
    return function (end, data) {
      if(end) return cb(null, sum)
      sum += data
      if(++i >= 10) {
        i = 0
        cb(null, sum)
      }
    }
  }
}

pull(
  pull.count(1000),
  everyTen(),
  pull.log()
)

Example: variable sized window

Each window doesn't have to be the same size...

var pull   = require('pull-stream')
var window = require('pull-window')

function groupTo100 () {
  var sum = null
  return window(function (_, cb) {
    if(sum != null) return

    //sum stuff together until you have 100 or more
    return function (end, data) {
      if(end) return cb(null, sum)
      sum += data
      if(sum >= 100) {
        //copy sum like this, incase the next item
        //comes through sync
        var _sum = sum; sum = null
        cb(null, _sum)
      }
    }
  })
}

pull(
  pull.count(1000)
  groupTo100(),
  pull.log()
)

Example: sliding window

to make more over lapping windows just return the window function more often.

var pull   = require('pull-stream')
var window = require('pull-window')

function sliding () {
  return window(function (_, cb) {
    var sum = 0, i = 0

    //sum stuff together until you have 100 or more
    return function (end, data) {
      if(end) return cb(null, sum)
      sum += data
      if(++i >= 10) {
        //in this example, each window gets it's own sum,
        //so we don't need to copy it.
        cb(null, sum)
      }
    }
  })
}

pull(
  pull.count(100)
  sliding(),
  pull.log()
)

API

window (start, map)


window(function startWindow (data, cb) {

  //called on each chunk
  //including the first one
  return function addToWindow (end, data) {
    //cb(null, aggregate) when done.
  }
}, function mapWindow (start, data) {
  //(optional)
  //map the window to something that tracks start, also
})

By default, windows are mapped to {start: firstData, data: aggregate}. unless you pass in an different mapWindow function.

window.sliding(reduce, size)

reduce every size items into a single value, in a sliding window

window.recent(size, time)

tumbling window that groups items onto an array, either every size items, or within time ms, which ever occurs earliest.

License

MIT

FAQs

Last updated on 22 May 2016

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