Sequential Object Stream Joiner (SOSJ) -- Provides an align function that can be used as a precursor to joining two objectMode streams.

Combines two objectMode streams that are each ALREADY ORDERED by a sequence key and emits a new stream which is doublets of records for the two joined streams.

If you wish to use floating points keys, then you must use the optional epsilon param, which follows the classical semantics for float-comparison.

You can then use other Transform streams to perform typical Set join operations. Or you can use some that have already been created for you that wrap this library: stream-joins

var align = require("sosj")
var spy = require("through2-spy")
var spigot = require("stream-spigot")

var left = spigot({objectMode: true}, [
  {v: 0, foo: 100},
  {v: 1, foo: 200},
  {v: 2, foo: 300},
  {v: 3, foo: 400},
  {v: 4, foo: 500},
])

var right = spigot({objectMode: true}, [
  {v: 0, bar: 100},
  {v: 2, bar: 200},
  {v: 4, bar: 300},
  {v: 8, bar: 400},
])

align("v", left, right).pipe(spy({objectMode: true}, console.log))

/*
[ { v: 0, foo: 100 }, { v: 0, bar: 100 } ]
[ { v: 1, foo: 200 }, null ]
[ { v: 2, foo: 300 }, { v: 2, bar: 200 } ]
[ { v: 3, foo: 400 }, null ]
[ { v: 4, foo: 500 }, { v: 4, bar: 300 } ]
[ null, { v: 8, bar: 400 } ]
 */

Align the two streams by sequenceKey into doublets of [left, right], [left, null], or [null, right] depending on if the records have matching sequenceKey values. If epsilon param is used, floating-number comparison semantics are triggered, i.e., keys will match if Math.abs(key_left - key_right) <= epsilon

MIT