timestream-filters

Filter functions for sequential objectMode data, e.g. timeseries data.

var spigot = require("stream-spigot")
var concat = require("concat-stream")

var filters = require("timestream-filters")

function stream() {
  return spigot({objectMode: true}, [
    {v: 50, foo: 150},
    {v: 100, foo: 1100},
    {v: 150, foo: 1150},
    {v: 250, foo: 1250},
    {v: 500, foo: 1500},
    {v: 550, foo: 1550},
  ])
}

stream().pipe(filters.range("v", 120, 500)).pipe(concat(console.log))

/*
[ { v: 150, foo: 1150 },
  { v: 250, foo: 1250 },
  { v: 500, foo: 1500 } ]
 */

stream().pipe(filters.rtrim(3)).pipe(concat(console.log))

/*
[ { v: 250, foo: 1250 },
  { v: 500, foo: 1500 },
  { v: 550, foo: 1550 } ]
 */

stream().pipe(filters.ltrim(3)).pipe(concat(console.log))

/*
[ { v: 50, foo: 150 },
  { v: 100, foo: 1100 },
  { v: 150, foo: 1150 } ]
 */

function fifties(record) {
  return ((record.foo / 50) % 2) == 0
}

stream().pipe(filters.filter(fifties)).pipe(concat(console.log))

/*
[ { v: 100, foo: 1100 },
  { v: 500, foo: 1500 } ]
 */

API

timestream-filters provides four filtering transforms for ordered objectMode streams.

• range
• rtrim
• ltrim
• scrub
• filter

range(seqKey, start, end)

Only forward records where the sequence key seqKey is between start and end inclusively to downstream.

rtrim(n)

Trim the stream to n records from the right, e.g. the latest n records.

ltrim(n)

Trim the stream to n records from the left, e.g. the first n records.

scrub()

Remove any records that are "empty", that is they have no data beyond the timestamp.

filter(fn)

Generically filter the stream. Provide a function fn(record) that returns true to keep the record for false to discard it.

LICENSE

MIT