Generate json object from array of dates with occurences of each date

Question

Hello I have a list of dates, stored in an array; there are multiple entries for the same date. I want to get the occurrences of each date in the for of json object, something like :

Expected output: dates:[{date:11/10/2019,count: 5},{date: 11/11/2019,count:4},{date:11/12/2019, count: 5 }]

My array data looks like:

[
  "11/10/2019, 10:44:16 PM",
  "11/10/2019, 10:48:26 AM",
  "11/10/2019, 10:59:41 PM",
  "11/10/2019, 11:37:53 AM",
  "11/10/2019, 12:19:52 PM",
  "11/11/2019, 12:46:59 PM",
  "11/11/2019, 12:59:08 PM",
  "11/11/2019, 1:32:23 PM",
  "11/11/2019, 3:08:01 AM",
  "11/12/2019, 3:21:39 AM",
  "11/12/2019, 3:26:00 PM",
  "11/12/2019, 3:27:13 PM",
  "11/12/2019, 4:43:24 AM",
  "11/12/2019, 4:49:39 PM"
]

I like to consider only the date in the json.

I tried code:

var cur;
var cnt = 0;
for (var i = 0; i < array_dates.length; i++) {
    cur = current.getDate();
    var d = new Date(array_dates[i]);
    var n = d.getDate();
    if (n != cur) {
        if (cnt > 0) {
            newdata[current] = cnt;
        }
        current = new Date(array_dates[i]);
        cnt = 1;
    } else {
        cnt++;
    }
}
newdata = JSON.stringify(newdata);

But I don't get an object in the expected way. I am missing something but not sure how to fix. How can I achieve the desired result with the array?

Have you searched for Group by? with little modification you can do it — Prashant Pimpale
– Prashant Pimpale, Commented Nov 6, 2019 at 11:35
@PrashantPimpale no..how can i perform it on my array as the examples i saw are kind of json arrays and have key values, so is it possible to do it in my example. — sina123
– sina123, Commented Nov 6, 2019 at 11:38

Prashant Pimpale · Accepted Answer · 2019-11-06 12:19:38Z

Another one:

var array = [
    "11/10/2019 10:44:16 PM",
    "11/10/2019 10:44:16 PM",
    "11/10/2019 10:43:06 PM",
    "11/10/2019 10:41:16 PM",
    "11/10/2019 10:40:16 PM",
    "11/11/2019 10:29:16 PM",
    "11/11/2019 10:28:16 PM",
    "11/11/2019 10:20:16 PM",
    "11/11/2019 10:29:16 PM",
    "11/12/2019 10:23:16 PM",
    "11/12/2019 10:20:16 PM",
    "11/12/2019 10:19:16 PM",
    "11/12/2019 10:21:16 PM",
    "11/12/2019 10:18:16 PM"
]

var result = [];

array.reduce(function(respObj, value) {
    value = value.substring(0, 10);
    if (!respObj[value]) {
        respObj[value] = {
            Date: value,
            Count: 1
        };
        result.push(respObj[value])
    } else {
        respObj[value].Count++;
    }
    return respObj;
}, {});

console.log(result)

Nick · Accepted Answer · 2019-11-06 12:01:06Z

You can use String.split to get the date portion of the string (to the left of the comma) and then count each value into an object, then processing the counts to produce an output in the form you desire:

const array_dates = [
  "11/10/2019, 10:44:16 PM",
  "11/10/2019, 10:48:26 AM",
  "11/10/2019, 10:59:41 PM",
  "11/10/2019, 11:37:53 AM",
  "11/10/2019, 12:19:52 PM",
  "11/11/2019, 12:46:59 PM",
  "11/11/2019, 12:59:08 PM",
  "11/11/2019, 1:32:23 PM",
  "11/11/2019, 3:08:01 AM",
  "11/12/2019, 3:21:39 AM",
  "11/12/2019, 3:26:00 PM",
  "11/12/2019, 3:27:13 PM",
  "11/12/2019, 4:43:24 AM",
  "11/12/2019, 4:49:39 PM"
];


let counts = array_dates.reduce((c, v) => {
  let d = v.split(',')[0];
  c[d] = (c[d] || 0) + 1;
  return c;
}, {});
let data = {
  dates: []
};
for (date in counts) {
  data.dates.push({
    date: date,
    count: counts[date]
  });
}
console.log(data);

Nice answer but is the order of the dates guaranteed to stay the same? ref
It should as properties in counts will be created (and then processed) in the same order as the dates are encountered in array_dates. But, I don't have sufficiently in-depth knowledge of how JS works to guarantee that.

ibrahim mahrir · Accepted Answer · 2019-11-06 11:53:31Z

var counts = [];                                       // the result array
var hash = {};                                         // The hash will map a date to an index in the result array 'counts'

for(var i = 0; i < array_dates.length; i++) {          // for each date in array_dates
  var date = array_dates[i].slice(0, 10);              // get the date part alone (a simple slice will do)

  if(hash.hasOwnProperty(date)) {                      // check if the hash contains an entry for this date
    counts[hash[date]].count++;                        // if so get the object of this date and increment its count
  } else {                                             // otherwise
    hash[date] = counts.push(                          // create a new object for this date
      { date: date, count: 1 }                         // ... initialize its count to 1
    ) - 1;                                             // ... and add the index to 'hash' (push will return the new length so the last index is the new length - 1)
  }
}

Example:

var array_dates = [ "11/10/2019, 10:44:16 PM", "11/10/2019, 10:48:26 AM", "11/10/2019, 10:59:41 PM", "11/10/2019, 11:37:53 AM", "11/10/2019, 12:19:52 PM", "11/11/2019, 12:46:59 PM", "11/11/2019, 12:59:08 PM", "11/11/2019, 1:32:23 PM", "11/11/2019, 3:08:01 AM", "11/12/2019, 3:21:39 AM", "11/12/2019, 3:26:00 PM", "11/12/2019, 3:27:13 PM", "11/12/2019, 4:43:24 AM", "11/12/2019, 4:49:39 PM" ];

var counts = [];
var hash = {};

for(var i = 0; i < array_dates.length; i++) {
  var date = array_dates[i].slice(0, 10);

  if(hash.hasOwnProperty(date)) {
    counts[hash[date]].count++;
  } else {
    hash[date] = counts.push(
      { date: date, count: 1 }
    ) - 1;
  }
}

console.log(counts);

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