terriajs/lib/Core/combineData.js

Geospatial data visualization platform.

'use strict';

/**
 * Combines two data arrays, each with the format [[x1, y1], [x2, y2], ...]
 * maintaining the order of the x's.
 * The x and y can be anything with order (integers, floats, dates, etc)
 * @param  {Array} array Array of arrays, eg. [[[x1, y1], [x2, y2]], [[a1, b1], [a2, b2]]]
 * @return {Number[]|Date[]} Combined array.
 */
function combineData(arrays) {
    // This implementation works, but could be streamlined.
    var numArrays = arrays.length;
    if (numArrays === 1) {
        return arrays[0];
    }
    var expandedArrays = arrays.map(function(array, arrayIndex) {
        return array.map(function(a) {
            var element = nullArray(numArrays + 1);
            element[0] = a[0];
            element[arrayIndex + 1] = a[1];
            return element;
        });
    });
    var result = Array.prototype.concat.apply([], expandedArrays);
    result.sort(compareFunction);
    for (var i = result.length - 2; i >= 0; i--) {
        if (compareFunction(result[i], result[i + 1]) === 0) {
            // merge the two rows and delete the old one
            result[i] = mergeElements(result[i], result[i + 1]);
            result.splice(i + 1, 1);
        }
    }
    return result;
}

function compareFunction(a, b) {
    return a[0] - b[0];
    // should be the same as:
    // if (a[0] < b[0]) {
    //     return -1;
    // }
    // if (a[0] > b[0]) {
    //     return 1;
    // }
    // return 0;
}

function nullArray(len) {
    return Array.apply(null, new Array(len)).map(function() { return null; });
}

function mergeElements(e, f) {
    // eg. e = [1, null, null, 0] and f = [1, 15, null, null] should give [1, 15, null, 0]
    return e.map(function(a, i) {
        return (a === null ? f[i] : a);
    });
}

module.exports = combineData;