Moving Sum

Computes a moving sum over an array.

Installation

$ npm install compute-msum

For use in the browser, use browserify.

Usage

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

msum( arr, window[, options] )

Slides a window over an array to compute a moving sum. For numeric arrays,

var arr = [ 1, 2, 3, 4, 5 ];

var values = msum( arr, 2 );
// returns [ 3, 5, 7, 9 ]

The function accepts two options:

• copy: boolean indicating whether to return a new array containing the computed sums. Default: true.
• accessor: accessor function for accessing values in object arrays.

To mutate the input array (e.g., when input values can be discarded or when optimizing memory usage), set the copy option to false.

var arr = [ 1, 2, 3, 4, 5 ];

var values = msum( arr, 2, {
	'copy': false
});
// returns [ 3, 5, 7, 9 ]

console.log( arr === values );
// returns true

For non-numeric arrays, provide an accessor function for accessing numeric array values.

var arr = [
	{'x':1},
	{'x':2},
	{'x':3},
	{'x':4}
];

function getValue( d ) {
	return d.x;
}

var values = msum( arr, 2, {
	'accessor': getValue
});
// returns [ 3, 5, 7 ]

Note: the returned array has length L - W + 1, where L is the length of the input array and W is the window size.

Examples

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

var data = new Array( 50 );
for ( var i = 0; i < data.length; i++ ) {
	data[ i ] = Math.random() * 100;
}
var values = msum( data, 8 );
console.log( values.join( '\n' ) );

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. Rebekah Smith.