ema-stream

ema-stream

Exponential moving average from a stream. Module and command line.

example - module

numbers source

var emaStream = require('ema-stream');

var ema = emaStream();

var count = 0;
function source () {
  var r = count++;
  ema.write(r.toString() + '\n');
}

setInterval(source, 100);

ema.on('readable', function () {
  ema.pipe(process.stdout);
})

output

3
10
18
etc

json source

var emaStream = require('ema-stream');

var ema = emaStream({
  pluck: ['key1', 'key2']
});

var count = 0;
function source () {
  var obj = {
    key1: count++,
    key2: Math.random() * 500
  };

  ema.write(JSON.stringify(obj) + '\n');
}

setInterval(source, 100);

ema.on('readable', function () {
  ema.pipe(process.stdout);
});

output

{"key1":3,"key2":232}
{"key1":10,"key2":245}
{"key1":18,"key2":210}
etc.

methods

var emaStream = require('ema-stream');

var ema = emaStream(opts)

Create a new stream instance ema with options opts:

• opts.window: 60000 - Length of window in ms.
• opts.pluck: null - Keys to pluck from incoming JSON. If unspecified, incoming chunks is assumed to be numbers.
• opts.integers: true - Whether to round output.
• opts.refreshEvery: 1000 - How often to emit current average in ms.
• opts.emitFirstValue: false - Whether to emit on the first value or wait until the first window has passed to emit the first time.

example - command line

numbers source

$ counter
0
1
2
3
^C

$ counter | ema-stream
3 # Output is refreshed every second. 3, 10, 19, 28, etc.

json source

$ tail -f logfile.log
{"type":"request","statusCode":200,"wallTime":27,"dbConnections":40}
{"type":"request","statusCode":200,"wallTime":45,"dbConnections":42}
{"type":"request","statusCode":200,"wallTime":207,"dbConnections":48}
{"type":"request","statusCode":200,"wallTime":205,"dbConnections":50}
^C

# Pluck only the keys we're interested in.
$ tail -f logfile.log | ema-stream --pluck wallTime,dbConnections
{"wallTime":62,"dbConnections":42} # Ouput is refreshed every second.

arguments

$ ema-stream \
  --window 60000 # Window to calculcate moving average from in ms.
  --integers true # Whether to round output.
  --refreshEvery 1000 # How often to refresh current average in ms.
  --pluck # Comma-separated list of keys to pluck from incoming JSON. If
  unspecified, input is assumed to be numbers.
  --emitFirstValue false # Whether to emit on the first value or wait
  until the first window has passed to emit the first time.