compute-datespace

1.0.1 • Public • Published

datespace

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Generates an array of linearly spaced dates.

Installation

$ npm install compute-datespace

For use in the browser, use browserify.

Usage

To use the module,

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

datespace( start, stop[, length, opts] )

Generates an array of linearly spaced Date objects. If a length is not provided, the default output array length is 100.

var stop = '2014-12-02T07:00:54.973Z',
    start = new Date( stop ) - 60000;
 
var arr = datespace( start, stop, 6 );
/* returns [
    'Mon Dec 01 2014 22:59:54 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:06 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:18 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:30 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:42 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:54 GMT-0800 (PST)'
]
*/

The start and stop times may be either Date objects, date strings, Unix timestamps, or JavaScript timestamps.

var start, stop, arr;
 
// JavaScript timestamps:
stop = 1417503654973;
start = new Date( stop - 60000 );
 
arr = datespace( start, stop, 6 );
/* returns [
    'Mon Dec 01 2014 22:59:54 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:06 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:18 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:30 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:42 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:54 GMT-0800 (PST)'
]
*/
 
// Unix timestamps:
stop = 1417503655;
start = stop - 60;
 
arr = datespace( start, stop, 6 );
/* returns [
    'Mon Dec 01 2014 22:59:54 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:06 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:18 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:30 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:42 GMT-0800 (PST)',
    'Mon Dec 01 2014 23:00:54 GMT-0800 (PST)'
]
*/

The output array is guaranteed to include the start and end times. Beware, however, that values between the start and end are subject to rounding errors. For example,

var arr = datespace( 1417503655000, 1417503655001, 3 );
// returns [ 1417503655000, 1417503655000, 1417503655001 ]

where sub-millisecond values are truncated by the Date constructor. Duplicate values should only be a problem when the interval separating consecutive times is less than a millisecond. As the interval separating consecutive dates goes to infinity, the quantization noise introduced by millisecond resolution is negligible.

By default, fractional timestamps are floored. To specify that timestamps always be rounded up or to the nearest millisecond when converted to Date objects, set the round option (default: floor).

// Equivalent of Math.ceil():
var arr = datespace( 1417503655000, 1417503655001, 3, { 'round': 'ceil' } );
// returns [ 1417503655000, 1417503655001, 1417503655001 ]
 
// Equivalent of Math.round():
var arr = datespace( 1417503655000, 1417503655001, 3, { 'round': 'round' } );
// returns [ 1417503655000, 1417503655001, 1417503655001 ]

Notes

This function is similar to compute-linspace.

Examples

var datespace = require( 'compute-datespace' ),
    start,
    stop,
    arr;
 
stop = '2014-12-02T07:00:54.973Z';
start = new Date( stop ) - 100000;
 
// Default behavior:
arr = datespace( start, stop );
console.log( arr.join( '\n' ) );
 
// Specify length:
arr = datespace( start, stop, 10 );
console.log( arr.join( '\n' ) );
 
arr = datespace( start, stop, 11 );
console.log( arr.join( '\n' ) );
 
// Create an array with decremented values:
arr = datespace( stop, start, 11 );
console.log( arr.join( '\n' ) );

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

$ node ./examples/index.js

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.


Copyright

Copyright © 2014. Athan Reines.

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