# compute-hmean

Computes the harmonic mean over an array of values.

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compute-hmean
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Harmonic Mean
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Computes the harmonic mean over an array of values.

## Installation

``\$ npm install compute-hmean``

## Usage

The use the module,
``var hmean = require( 'compute-hmean' );``

#### hmean( arr )

Computes the harmonic mean.
``````var data = [ 1, 5, 3, 4, 16 ];

var mu = hmean( 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 hmean = require( 'compute-hmean' );

var data = new Array( 1000 );

for ( var i = 0; i < data.length; i++ ) {
data[ i ] = Math.random() * 100;
}

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

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

## Notes

For arrays exceeding memory constraints, you are encouraged to use streams; see flow-hmean.

## 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``