Get Data From Array Javascript

Question

I have an array with different amounts of data, I want to replace the period contents of the array with the data I want for example:

Data array from key 0 to 4 of the period must contain "2010-10-10".
data array from key 5 to 10 period must contain "2010-11-11"

Condition: I need an array of data from 0-4, 5-9, 10-14 (multiples of 5) The following data I have:

[
     {
         "id": "1",
         "name": "SUNARTA",
         "period":"",
     },
     {
         "id": "2",
         "name": "AAN",
         "period":"",
     },
     {
         "id": "3",
         "name": "MIKO",
         "period":"",
     },
     {
         "id": "4",
         "name": "NIKA",
         "period":"",
     },
     {
         "id": "5",
         "name": "LALA",
         "period":"",
     },
     {
         "id": "6",
         "name": "MMAAN",
         "period":"",
     },
    {
     "id": "7",
     "name": "NINA",
     "period":"",
 }
]

This is my code:

for (var i = 0; i < element.length; i++) {
  var datePeriod = new Date(req.body.start);
  var periode = datePeriod;

  if (i % 5 == 0) {
    datePeriod.setDate(datePeriod.getDate() + 1);
    element[i].periode = periode;

  } else {
    element[i].periode = periode;
  }
}

I want data should be:

[
 {
     "id": "1",
     "name": "SUNARTA",
     "period":"2010-10-10",
 },
 {
     "id": "2",
     "name": "AAN",
     "period":"2010-10-10",
 },
 {
     "id": "3",
     "name": "MIKO",
     "period":"2010-10-10",
 },
 {
     "id": "4",
     "name": "NIKA",
     "period":"2010-10-10",
 },
 {
     "id": "5",
     "name": "LALA",
     "period":"2010-10-10",
 },
 {
     "id": "6",
     "name": "MMAAN",
     "period":"2011-11-11",
 },
 {
     "id": "7",
     "name": "NINA",
     "period":"2011-11-11",
 },
 ]

"Data array from key 0 to 4 of the period contains "2010-10-10"" but not in the sample data you posted. — RobG
– RobG, Commented Nov 22, 2018 at 9:24
You could use .map() which take a predicate as argument (basically a function), so you can make a filter in it (if e.period === ?), then make your changes there. — Izio
– Izio, Commented Nov 22, 2018 at 9:24
@RobG yes because it was initially empty, and I will fill it in the conditions that will be created because the array data from data 0 - 4 are the same, 5-9 contents are different from data 0-4 — Lely Suju
– Lely Suju, Commented Nov 22, 2018 at 9:26

RobG · Accepted Answer · 2018-11-22 22:30:29Z

You are very close to a solution. Your issue is that you're reinitialising datePeriod on each loop. You only need to do that once, then increment it on every 5th element. So move the initialisation outside the for loop (and tidy a few other things):

var element = [{"id": "1","name": "SUNARTA","period": ""},
               {"id": "2","name": "AAN","period": ""},
               {"id": "3","name": "MIKO","period": ""},
               {"id": "4","name": "NIKA","period": ""},
               {"id": "5","name": "LALA","period": ""},
               {"id": "6","name": "MMAAN","period": ""},
               {"id": "7","name": "NINA","period": ""}];

// Helper to format the date
function formatDate(d) {
  return `${d.getFullYear()}-${('0'+d.getMonth()).slice(-2)}-${('0'+d.getDate()).slice(-2)}`;
}

// Initialise datePeriod outside the loop
var datePeriod = new Date();

for (var i = 0; i < element.length; i++) {
  // This variable is unnecessary
  //var periode = datePeriod;

  // Increment datePeriod every 5th element
  // The else loop isn't necessary
  if (i && i % 5 == 0) {
    datePeriod.setDate(datePeriod.getDate() + 1);
  }
  element[i].period = formatDate(datePeriod);
}

console.log(element)

This creates just one Date object, so it will be reasonably efficient.

Hassan Imam · Accepted Answer · 2018-11-22 14:06:24Z

1

You can use array#map and iterate through each object based on the index increment date after every 5 iteration and update the period property.

const data = [ { "id": "1", "name": "SUNARTA", "period":"", }, { "id": "2", "name": "AAN", "period":"", }, { "id": "3", "name": "MIKO", "period":"", }, { "id": "4", "name": "NIKA", "period":"", }, { "id": "5", "name": "LALA", "period":"", }, { "id": "6", "name": "MMAAN","period":"", }, { "id": "7", "name": "NINA", "period":"", }],
    size = 5,
    startDate = '2010-10-10',
    result = data.map((o,i) => {
      let index = Math.floor(i/size);
      let period = i == 0 ? new Date(startDate) : 
      (date => (new Date(date.setDate(date.getDate() + index))))(new Date(startDate));
      period = period.toISOString().substring(0,10);
      return {...o, period};
    },[]);
console.log(result);

edited Nov 22, 2018 at 14:06

answered Nov 22, 2018 at 9:32

Hassan Imam

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1 Comment

RobG Over a year ago

toISOString returns the UTC date, so will be the wrong date depending on the host timezone offset.

HMR · Accepted Answer · 2018-11-23 07:41:16Z

If you want to increase the date with one day for every 5 items then you can do the following:

A function that takes a start date and a number (index of the array) and add days to the start date depending on the number:

function calcDate(startDate, i) {
  return formatDate(
    new Date(
      new Date(startDate).setDate(
        //add a day every 5 days
        startDate.getDate() + Math.floor(i / 5),
      ),
    ),
  );
}

Now create a variable holding the start date: var date = new Date();

Use Array.prototype.map to map the array you have to create a new array where period is set with the result of the calculate date function passing in the start date and the index of the current item:

var result = data.map(function(d, i) {
  return Object.assign({}, d, {
    period: calcDate(date, i),
  });
});

Complete code:

var data = [{"id":"1","name":"SUNARTA","period":""},{"id":"2","name":"AAN","period":""},{"id":"3","name":"MIKO","period":""},{"id":"4","name":"NIKA","period":""},{"id":"5","name":"LALA","period":""},{"id":"6","name":"MMAAN","period":""},{"id":"7","name":"NINA","period":""}];

function pad(num) {
  return ('000' + num).slice(-2);
}
function formatDate(date) {
  return [
    date.getFullYear(),
    pad(date.getMonth() + 1),
    pad(date.getDate()),
  ].join('-');
}
function calcDate(startDate, i) {
  return formatDate(
    new Date(
      new Date(startDate).setDate(
        //add a day every 5 days
        startDate.getDate() + Math.floor(i / 5),
      ),
    ),
  );
}
var date = new Date();
var result = data.map(function(d, i) {
  return Object.assign({}, d, {
    period: calcDate(date, i),
  });
});
console.log(result);

toISOString returns the UTC date, so will be the wrong date depending on the host timezone offset.

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