What could be causing the excessive number of entries in my mapping results?

Question

What could be causing the excessive number of entries in my mapping results?

I am in need of mapping an array consisting of dates. Each date within this array is associated with a group of dates (formatted as an array).

For instance: The format array looks like this:

let format = [3, 3, 1, 5, 4, 4, 3, 5, 13, 10, 3, 5, 5, 2, 2, 10];

This indicates that the first three dates in the dates array belong to one group, the next 3 dates belong to another group, and so on.

Therefore, I expect my output to consist of 16 items (matching the length of the format array). The desired output would look something like this: For the first group of dates: Start: lowest date in that group End: highest date in that group

However, the current output is simply returning entries based on the number of dates.

let format = [3, 3, 1, 5, 4, 4, 3, 5, 13, 10, 3, 5, 5, 2, 2, 10];
let dates = [
  // Insert sample dates here
];

var numTimesUsed = 0;
var nameIndex = 0;
let app_multiple = dates.map(function combineTitleData(dataItem, index) {
  if (format[nameIndex] == numTimesUsed) {
    nameIndex++;
    numTimesUsed = 0;
  }
  numTimesUsed++;
  let end = new Date(dates[nameIndex]);
  end.setDate(end.getDate() + parseInt(format[nameIndex]) - 1);
  return {
    start: dates[nameIndex],
    end: end
  };
});
//
console.log(app_multiple);

Thank you

javascript arrays

Answer 1

Answer №1

Using the Splice method will help retrieve specific groups from an array.

const res = format.map(num => dates.splice(0,num))

let format = [3, 3, 1, 5, 4, 4, 3, 5, 13, 10, 3, 5, 5, 2, 2, 10];
let dates = [ "2021-10-04T04:00:00.000Z", "2021-10-05T04:00:00.000Z", "2021-10-06T04:00:00.000Z", ... (omitted for brevity)]

const res = format.map(num => {
  const arr = dates.splice(0,num)
  const start = arr.shift();
  const end = arr.length === 0 ? start : arr.pop();
  return { start, end }
})
console.log(res)

To obtain an array of objects containing start and end values (only start if no end), you can implement this solution - assuming the date strings are sorted. If unsorted, simply use dates.sort() to sort them.

const res = format.map(num => {
  const arr = dates.splice(0, num)
  const start = arr.shift();
  const end = arr.length === 0 ? "" : arr.pop(); 
  return end ? { start, end } : { start }
})
console.log(res)

let format = [3, 3, 1, 5, 4, 4, 3, 5, 13, 10, 3, 5, 5, 2, 2, 10];
let dates = [ "2021-10-04T04:00:00.000Z", "2021-10-05T04:00:00.000Z", "2021-10-06T04:00:00.000Z", ... (omitted for brevity)]

const res = format.map(num => {
  const arr = dates.splice(0, num)
  const start = arr.shift();
  const end = arr.length === 0 ? "" : arr.pop()
  return end ? { start, end } : { start }
})
console.log(res)

Alternatively, set start and end to the same value if only one date is present:

const res = format.map(num => {
  const arr = dates.splice(0, num)
  const start = arr.shift();
  const end = arr.length === 0 ? start : arr.pop(); 
  return { start, end }
})
console.log(res)

Answer 2

Using the Splice method will help retrieve specific groups from an array.

const res = format.map(num => dates.splice(0,num))

let format = [3, 3, 1, 5, 4, 4, 3, 5, 13, 10, 3, 5, 5, 2, 2, 10];
let dates = [ "2021-10-04T04:00:00.000Z", "2021-10-05T04:00:00.000Z", "2021-10-06T04:00:00.000Z", ... (omitted for brevity)]

const res = format.map(num => {
  const arr = dates.splice(0,num)
  const start = arr.shift();
  const end = arr.length === 0 ? start : arr.pop();
  return { start, end }
})
console.log(res)

To obtain an array of objects containing start and end values (only start if no end), you can implement this solution - assuming the date strings are sorted. If unsorted, simply use dates.sort() to sort them.

const res = format.map(num => {
  const arr = dates.splice(0, num)
  const start = arr.shift();
  const end = arr.length === 0 ? "" : arr.pop(); 
  return end ? { start, end } : { start }
})
console.log(res)

let format = [3, 3, 1, 5, 4, 4, 3, 5, 13, 10, 3, 5, 5, 2, 2, 10];
let dates = [ "2021-10-04T04:00:00.000Z", "2021-10-05T04:00:00.000Z", "2021-10-06T04:00:00.000Z", ... (omitted for brevity)]

const res = format.map(num => {
  const arr = dates.splice(0, num)
  const start = arr.shift();
  const end = arr.length === 0 ? "" : arr.pop()
  return end ? { start, end } : { start }
})
console.log(res)

Alternatively, set start and end to the same value if only one date is present:

const res = format.map(num => {
  const arr = dates.splice(0, num)
  const start = arr.shift();
  const end = arr.length === 0 ? start : arr.pop(); 
  return { start, end }
})
console.log(res)

Answer 3

Answer №2

Map always guarantees the same number of inputs as outputs, so when dealing with dates, don't expect the output array to match the length of the input. To address this issue, we utilize the format as an input parameter for the map function to obtain an array collection.

let format = [3, 3, 1, 5, 4, 4, 3, 5, 13, 10, 3, 5, 5, 2, 2, 10];
let dates = [
  "2021-10-04T04:00:00.000Z",
  ...
  "2022-01-18T04:00:00.000Z"
];

// Convert strings into dates for comparison
const realDates = dates.map(d => new Date(d));

// Apply map on the format array since it always returns the same number of elements as the input array, hence guiding us to use format instead of dates
const dateGroup = format.map(num => realDates.slice(0,num));

// Iterate over the array to generate a new form
let app_multiple = dateGroup.map(function createNewObject(singleDateCollection, index) {

  return {
    start: new Date(Math.min.apply(null,singleDateCollection)),
    end: new Date(Math.max.apply(null,singleDateCollection))
  };
});
//
console.log(app_multiple);

Answer 4

Map always guarantees the same number of inputs as outputs, so when dealing with dates, don't expect the output array to match the length of the input. To address this issue, we utilize the format as an input parameter for the map function to obtain an array collection.

let format = [3, 3, 1, 5, 4, 4, 3, 5, 13, 10, 3, 5, 5, 2, 2, 10];
let dates = [
  "2021-10-04T04:00:00.000Z",
  ...
  "2022-01-18T04:00:00.000Z"
];

// Convert strings into dates for comparison
const realDates = dates.map(d => new Date(d));

// Apply map on the format array since it always returns the same number of elements as the input array, hence guiding us to use format instead of dates
const dateGroup = format.map(num => realDates.slice(0,num));

// Iterate over the array to generate a new form
let app_multiple = dateGroup.map(function createNewObject(singleDateCollection, index) {

  return {
    start: new Date(Math.min.apply(null,singleDateCollection)),
    end: new Date(Math.max.apply(null,singleDateCollection))
  };
});
//
console.log(app_multiple);

What could be causing the excessive number of entries in my mapping results?

Answer №1

Answer №2

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