# compute-nanqmean

Computes the quadratic mean (root mean square) of an array of values ignoring any values which are not numeric.

## Stats

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compute-nanqmean
1.0.08 years ago8 years ago !NPM versionnpm-imagenpm-url !Build Statustravis-imagetravis-url !Coverage Statuscoveralls-imagecoveralls-url !Dependenciesdependencies-imagedependencies-url
Computes the quadratic mean (root mean square) of an array of values ignoring any values which are not numeric.

## Installation

``\$ npm install compute-nanqmean``

For use in the browser, use browserify.

## Usage

To use the module,
``var nanqmean = require( 'compute-nanqmean' );``

#### nanqmean( arr )

Computes the quadratic mean (root mean square) ignoring non-numeric values.
``````var data = [ 2, 7, NaN, 3, -3, NaN, 9 ];

var mu = nanqmean( data );
// returns ~5.5136``````

## Examples

``````var nanqmean = require( 'compute-nanqmean' );

var data = new Array( 1000 );
for ( var i = 0; i < data.length; i++ ) {
if ( i%5 === 0 ) {
data[ i ] = NaN;
} else {
data[ i ] = Math.random() * 100;
}
}

console.log( nanqmean( data ) );``````

To run the example code from the top-level application directory,
``\$ node ./examples/index.js``

## Notes

1. The algorithm to compute the quadratic mean first calculates the L2 norm before dividing by the square root of the `array` length. This particular implementation attempts to avoid overflow and underflow and is accurate to `<1e-13` compared to the canonical formula for calculating the root mean square.
2. The quadratic mean of an `array` containing non-numeric values is equal to the quadratic mean of an equivalent `array` which contains only the numeric values. Hence,

``````var d1 = [ 1, NaN, 2, 3, NaN ],
d2 = [ 1, 2, 3 ];

console.log( nanqmean( d1 ) === nanqmean( d2 ) );
// returns true``````

## References

• Dahlquist, Germund and Bjorck, Ake. Numerical Methods in Scientific Computing.
• Blue, James (1978) "A Portable Fortran Program To Find the Euclidean Norm of a Vector". ACM Transactions on Mathematical Software.
• Higham, Nicholas J. Accuracy and Stability of Numerical Algorithms, Second Edition.

This module implements a one-pass algorithm proposed by S.J. Hammarling.

## 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``