compute-msum/README.md

Computes a moving sum over an array.

Moving Sum
===
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> Computes a moving sum over an array.


## Installation

``` bash
$ npm install compute-msum
```

For use in the browser, use [browserify](https://github.com/substack/node-browserify).


## Usage

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

#### msum( arr, window[, options] )

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

``` javascript
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`.

``` javascript
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.

``` javascript
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

``` javascript
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,

``` bash
$ node ./examples/index.js
```


## Tests

### Unit

Unit tests use the [Mocha](http://mochajs.org) test framework with [Chai](http://chaijs.com) assertions. To run the tests, execute the following command in the top-level application directory:

``` bash
$ make test
```

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


### Test Coverage

This repository uses [Istanbul](https://github.com/gotwarlost/istanbul) as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

``` bash
$ make test-cov
```

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

``` bash
$ make view-cov
```


---
## License

[MIT license](http://opensource.org/licenses/MIT). 


## Copyright

Copyright &copy; 2014-2015. Rebekah Smith.


[npm-image]: http://img.shields.io/npm/v/compute-msum.svg
[npm-url]: https://npmjs.org/package/compute-msum

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[travis-url]: https://travis-ci.org/compute-io/msum

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[coveralls-url]: https://coveralls.io/r/compute-io/msum?branch=master

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[dependencies-url]: https://david-dm.org/compute-io/msum

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[github-issues-url]: https://github.com/compute-io/msum/issues