through2-* demo

README.md

Another quick demo of through2-map and through2-filter.

Objective

• create a stream of monotonically increasing integers
• filter out the even integers
• show the differences between pairwise odd numbers in stream

Sample output

B - A = DELTA
1 - 0 = 1
5 - 1 = 4
5 - 5 = 0
7 - 5 = 2
9 - 7 = 2
11 - 9 = 2
13 - 11 = 2
13 - 13 = 0
15 - 13 = 2
17 - 15 = 2
21 - 17 = 4

index.coffee

###
through2-* demo

* create a stream of monotonically increasing integers
* filter out the even integers
* show the differences between pairwise odd numbers in stream

###
spigot = require "stream-spigot"
filter = require "through2-filter"
map = require "through2-map"

obj =
  objectMode: true

randint = (max) -> Math.floor(Math.random() * (max + 1))

nums = (x + randint(1) for x in [0..20])    # [ 0, 1, 3, 3, 5, ... 19, 19, 21 ]

source = spigot(obj, nums)

odds = filter(obj, (x) -> x % 2)            # filter out evens

deltas = map obj, (x) ->
    d = x - (@prev or 0)                    # diff between x and prev
    result = "#{x} - #{@prev or 0} = #{d}"  # curr - prev = delta
    @prev = x
    result

console.log('B - A = DELTA')
source
  .pipe(odds)
  .pipe(deltas)
  .on('data', (d) -> console.log d)

package.json

{
  "name": "thru-demo",
  "version": "0.0.1",
  "description": "'through2-* demo'",
  "main": "index.js",
  "dependencies": {
    "through2-map": "~1.2.1",
    "through2-filter": "~1.3.1",
    "stream-spigot": "~3.0.3",
    "concat-stream": "~1.4.5"
  },
  "author": "J. Voigt",
  "license": "BSD-2-Clause"
}