# compute-nanhmean

Computes the harmonic mean of an array of values ignoring any values which are not numeric.

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compute-nanhmean
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nanhmean
!NPM versionnpm-imagenpm-url !Build Statustravis-imagetravis-url !Coverage Statuscoveralls-imagecoveralls-url !Dependenciesdependencies-imagedependencies-url
Computes the harmonic mean of an array of values ignoring any values which are not numeric.

## Installation

``\$ npm install compute-nanhmean``

For use in the browser, use browserify.

## Usage

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

#### nanhmean( arr )

Computes the harmonic mean ignoring non-numeric values.
``````var data = [ 1, 5, NaN, 3, 4, NaN, 16 ];

var mu = nanhmean( data );
// returns ~2.7088``````

Note: only calculate the harmonic mean for positive, real numbers.
If an `array` contains negative numbers, the harmonic mean is nonsensical. For example, consider `x = [ 3, -3, 4 ]`. The harmonic mean of `x` is `12`, while the arithmetic mean is `1.33333...`. The harmonic mean should never be greater than the arithmetic mean.
Similarly, if an `array` contains zero values, the harmonic mean is also zero: `1/0 --> infinity` and `1/infinity --> 0`. For example, consider `x = [ 0, 100, 1000, 10000 ]`. Using the textbook definition of the harmonic mean, the mean would be `0`, which, given `x`, does not make sense.
If an `array` contains elements less than or equal to `0`, the function returns `NaN`.

## Examples

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

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( nanhmean( data ) );``````

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

## Notes

The harmonic mean of an array containing non-numeric values is equal to the harmonic 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( nanhmean( d1 ) === nanhmean( d2 ) );
// returns true``````

## 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``