Javascript push into array by index while looping through it

Question

var arr = [{
                        date : "2016/1/26",
                        count: 6
                    },
                    {
                        date : "2016/1/31",
                        count: 2
                    },
                    {
                        date : "2016/2/2",
                        count: 4
                    }]

I need to have all the dates (each day) inside the array from the current minimal date to the current max date. If the day does not exist, i need to add a new object with count=0.

The array is already sorted by date.

In my example, the array should be converted to:

arr = [{
        date : "2016/1/26",
        count: 6
    },
               {
        date : "2016/1/27",
        count: 0
    },
    {
        date : "2016/1/28",
        count: 0
    },
    {
        date : "2016/1/29",
        count: 0
    },
    {
        date : "2016/1/30",
        count: 0
    },
    {
        date : "2016/1/31",
        count: 2
    },
    {
        date : "2016/2/1",
        count: 0
    },
    {
        date : "2016/2/2",
        count: 4
    }]

My approach:

    for (i = 0; i < arr.length-1; i++) { 

                    var prev = new Date(arr[i].date);
                    var next = new Date(arr[i+1].date);

                    if (prev.setTime(prev.getTime() + 86400000) != next) {
                        //86400000 equals a day in miliseconds

                        arr.splice(i+1, 0, {date: prev, count: 0});

                    }

      }

This makes an infinite loop? The website gets stuck..

Nina Scholz · Accepted Answer · 2016-03-19 17:24:12Z

A solution with a loop in the loop.

var arr = [{ date: "2016/1/26", count: 6 }, { date: "2016/1/31", count: 2 }, { date: "2016/2/2", count: 4 }],
    result = function (array) {
        var r = [],
            min = new Date(arr[0].date);

        array.forEach(function (a) {
            var aDate= new Date(a.date);
            while (min < aDate) {
                r.push({ date: min.getFullYear() + '/' + (min.getMonth() + 1) + '/' + min.getDate(), count: 0 });
                min.setTime(min.getTime() + 86400000);
            }
            r.push(a);
            min.setTime(aDate.getTime() + 86400000);
        });
        return r;
    }(arr);

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

Another attempt with an object for counting and two loops. I works for unsorted data.

var arr = [{ date: "2016/1/26", count: 6 }, { date: "2016/1/31", count: 2 }, { date: "2016/2/2", count: 4 }],
    result = function (array) {
        var r = [],
            min = new Date(arr[0].date),
            max = new Date(arr[0].date),
            object = {},
            d;

        array.forEach(function (a) {
            var x = new Date(a.date);
            if (!object[a.date]) {
                object[a.date] = { date: a.date, count: 0 };
                if (x < min) {
                    min = x;
                }
                if (x > max) {
                    max = x;
                }
            }
            object[a.date].count += a.count;
        });
        while (min <= max) {
            d = min.getFullYear() + '/' + (min.getMonth() + 1) + '/' + min.getDate();
            r.push(object[d] || { date: d, count: 0 });
            min.setTime(min.getTime() + 86400000);
        }
        return r;
    }(arr);

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

Loufylouf · Accepted Answer · 2016-03-19 17:07:20Z

1

The problem is in your comparison operator between the previous date + 1 day and the next date : they are always different ! Try to add some console.log() in your code and you will see. As you only consider days here, you should extract from prev and next the day, month and year and compare this.

To do so, you can for example use the toDateString function or, instead of adding 1 day to your prev variable, compute the difference between prev and next and see if it's greater than one day or not.

edited Mar 19, 2016 at 17:07

answered Mar 19, 2016 at 16:44

Loufylouf

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3 Comments

Egidi Over a year ago

You are right. But if I do that I am only adding one day for each gap between days. In my example I would only add 2016/1/27 and 2016/2/1, because the new objects are not being processed in the loop.

Loufylouf Over a year ago

Ha ok, it just struck me as obvious the reason for your infinite loop and only took a glance at your code. I'll edit considering this.

Loufylouf Over a year ago

Edit made, the problem was not at all what I was thinking.

Siderite Zackwehdex · Accepted Answer · 2016-03-19 17:18:07Z

0

Date is an object in Javascript, when you compare them with equal it compares the references to the objects. Use date.getTime() or +(date) to get a value you can compare.

answered Mar 19, 2016 at 17:18

Siderite Zackwehdex

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Comments

trincot · Accepted Answer · 2016-03-19 17:46:42Z

Your if condition is always true, because you are comparing two distinct date objects. Even though they might represent the same date, as they are different objects, they are considered not equal.

Here is some code that does the date-gap-filling you are looking for:

// date formatter
function dateFmt(dt) {
    return dt.getFullYear() + '/' + (dt.getMonth()+1) + '/' + dt.getDay();
}

// main function
function fillDateGaps(arr) {
    if (!arr.length) return; // detect invalid input
    var result = [];
    var i = 0;
    var arrDate = new Date(arr[0].date);
    var curDate = arrDate;
    while (true) {
        var obj = { date: dateFmt(curDate), count: 0 };
        result.push(obj);
        if (arrDate.getDate() === curDate.getDate()) {
            console.log(arrDate, i);
            obj.count = arr[i].count;
            i++;
            if (i >= arr.length) break; // all done
            arrDate = new Date(arr[i].date);
        }
        curDate.setDate(curDate.getDate()+1);
        console.log('cur', curDate);
    }
    return result;
}

// example data
var arr = [{
    date : "2016/1/26",
    count: 6
},
{
    date : "2016/1/31",
    count: 2
},
{
    date : "2016/2/2",
    count: 4
}];

// call function
var result = fillDateGaps(arr);

// Snippet: output result in readable format
document.write ('<pre>' + JSON.stringify(result, null, 4) + '</pre>');

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

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