Find closest matches in an array

find-nearest-matches.js

function findNearestMatches(data, target, windowSize) {
    /*
     * Find [windowSize] items closest to [target] value
     * 
     * var arr = [0,1,2,3,4,5];
     * findNearestMatches(arr, 2, 3)
     * -> [1,2,3]
     * findNearestMatches(arr, -5, 4)
     * -> [0,1,2.3]
     */
    if (data.length < windowSize) {
        return data;
    }
    var results = [];
    var middleIndex = Math.floor(windowSize / 2);
    var matchIndex = data.indexOf(target);
    var firstIndex;
    if (matchIndex === -1) {
        // get first index of an item > the target
        for (var z = 0; z < data.length; z++) {
            if (data[z] > target || z === data.length - 1) {
                matchIndex = z;
                break;
            }
        }
    }
    // start from the matched index - # of items to put it in the middle
    for (var x = (matchIndex - middleIndex); x <= matchIndex; x++) {
        if (data[x]) {
            if (firstIndex === undefined) {
                firstIndex = x;
            }
            results.push(data[x]);
        }
    }
    // add items to the right
    var lastItemIndex = matchIndex + (windowSize - results.length) + 1;
    for (var i = (matchIndex + 1); i < lastItemIndex; i++) {
        if (data[i]) {
            results.push(data[i]);
        }
    }
    // add some more on the left if it's a later match
    if (results.length < windowSize) {
        var diff = windowSize - results.length;
        for (var y = 1; y <= diff; y++) {
            if (data[firstIndex - y]) {
                results.push(data[firstIndex - y]);
            }
        }
    }
    return results.sort();
}

/*
 * test it with mocha
 */
var assert = require('assert');
var start_dates = [
    '2017-07-23T09:30:00',
    '2017-07-23T10:30:00',
    '2017-07-23T11:30:00',
    '2017-07-23T11:30:00',
    '2017-07-23T12:30:00',
    '2017-07-23T13:30:00',
    '2017-07-23T14:30:00',
    '2017-07-23T17:30:00',
    '2017-07-23T18:30:00',
    '2017-07-23T19:30:00',
    '2017-07-23T20:30:00'
];
var target = '2017-07-23T12:15:00';
describe('findNearestMatches', function() {
    it('returns the whole list when windowSize is larger than dataset length', function() {
        var sorted = findNearestMatches(start_dates, target, 90);
        assert.equal(sorted, start_dates);
    });
    it('can have a windowSize of 1', function() {
        var sorted = findNearestMatches(start_dates, target, 1);
        assert.equal(sorted.length, 1);
    });
    it('returns a list the same length as windowSize', function() {
        var sorted = findNearestMatches(start_dates, target, 5);
        assert.equal(sorted.length, 5);
        var sorted2 = findNearestMatches(start_dates, target, 3);
        assert.equal(sorted2.length, 3);
        var sorted3 = findNearestMatches(start_dates, target, 4);
        assert.equal(sorted3.length, 4);
    });
    it('puts matching goal in the middle', function() {
        var target2 = '2017-07-23T12:30:00';
        var sorted = findNearestMatches(start_dates, target2, 5);
        var sortedIndex = sorted.indexOf(target2);
        // in the array
        assert.notEqual(sortedIndex, -1);
        // in the middle
        assert.equal(Math.floor(sorted.length / 2), sortedIndex);
        // wasn't in the middle of original array
        assert.notEqual(sortedIndex, start_dates.indexOf(target2));
    });
    it('matches an item at the end; still returns windowSize length', function() {
        var target2 = '2017-07-23T20:30:00';
        var sorted = findNearestMatches(start_dates, target2, 5);
        assert.equal(sorted.length, 5);
    });
    it('matches an item at the beginning; still returns windowSize length', function() {
        var target2 = '2017-06-23T20:30:00';
        var sorted = findNearestMatches(start_dates, target2, 5);
        assert.equal(sorted.length, 5);
    });
});