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.

`` js
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...

` js
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.

` js
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




$3


` js

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.




$3

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

$3

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

License

MIT