incrmsum

Provides a method to compute a moving sum incrementally.

Installation

$ npm install compute-incrmsum

For use in the browser, use browserify.

Usage

var incrmsum = require( 'compute-incrmsum' );

incrmsum( window )

Returns an initialized method to compute a moving sum incrementally. window sets the window size, i.e., the number of values over which to compute a moving sum.

var msum = incrmsum( 3 );

msum( [value] )

If provided a value, the method updates and returns the sum of the current window. If not provided a value, the method returns the current sum.

var sum;

// Filling window...
sum = msum( 2 );
// sum is 2

msum( 3 );
// sum is 5

msum( 2 );
// sum is 7

// Window starts sliding...
msum( -2 );
// sum is 3

msum( 9 );
// sum is 9

sum = msum();
// returns 9

Notes

1. If values have not yet been provided to msum, msum returns null.
2. The first W-1 returned sums will have less statistical support than subsequent moving sums, as W values are needed to fill the window buffer. Until the window is full, the value returned equals the sum of all values provided thus far.

The use case for this module differs from the conventional vector implementation and the stream implementation. Namely, this module decouples the act of updating the moving sum from the act of consuming the moving sum.

Examples

var incrmsum = require( 'compute-incrmsum' );

// Initialize a method to calculate the moving sum incrementally:
var msum = incrmsum( 5 ),
	sum;

// Simulate some data...
for ( var i = 0; i < 1000; i++ ) {
	sum = msum( Math.random()*100 );
	console.log( sum );
}
sum = msum();
console.log( sum );

To run the example code from the top-level application directory,

$ node ./examples/index.js

Tests

Unit

Unit tests use the Mocha test framework with Chai assertions. To run the tests, execute the following command in the top-level application directory:

$ make test

All new feature development should have corresponding unit tests to validate correct functionality.

Test Coverage

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

$ make test-cov

Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,

$ make view-cov

License

MIT license.

Copyright

Copyright © 2014-2015. The Compute.io Authors.