Lower Midmean

Computes the lower interquartile mean (lower midmean) of a numeric array.

Installation

$ npm install compute-lmidmean

For use in the browser, use browserify.

Usage

To use the module,

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

lmidmean( arr[, sorted] )

Computes the lower midmean for a numeric array. This is computed by discarding all values above the median and calculating the mean of those values falling between the first and third quartiles.

Note: the input array must contain 6 or more elements.

var unsorted = [ 5, 6, 7, 2, 1, 8, 4, 3 ];

var mean = lmidmean( unsorted );
// returns 2.5

If the input array is already sorted in ascending order, set the optional second argument to true.

var sorted = [ 1, 2, 3, 4, 5, 6, 7, 8 ];

var mean = lmidmean( sorted, true );
// returns 2.5

Examples

var data = new Array( 100 );

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

console.log( lmidmean( data ) );

To run the example code from the top-level application directory,

$ node ./examples/index.js

Notes

If provided an unsorted input array, the function is O( N log(N) + m ), where N is the input array length and m is the number of values located between the first and third quartiles of the lower range. If the input array is already sorted in ascending order, the function is O(m).

The lower midmean includes the values located between but not including the first and third quartiles of the lower range. In the following examples, the values included in the lower midmean are in bold.

[1,2,3,4,5,6,7,8] —> lmidmean: 2.5
[1,2,3,4,5,6,7,8,9,10,11,12] —> lmidmean: 3.5

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.

compute-io / lmidmean