filter array based on another inside for loop

Question

I try to filter the array based on const array inside the for-loop, my problem is that my filtered array is not being saved.

The main array that I use:

const allHours = [
  "10:00",
  "11:00",
  "12:00",
  "13:00",
  "14:00",
  "15:00",
  "16:00",
  "17:00",
  "18:00",
  "19:00",
];
let availableHours=[];

I have an empty array when I catch an hour that is occupied. I want to filter out the hour and get back a new array with the same allHours without the filtering being applied.

for (let i = 0; i < 7; i++) {
  const date = moment().utc().add(i, "days");

  if (date.weekday() === 5 || date.weekday() === 6) {
    continue;
  } else {
    if (meetings.map(d => {
      if (moment(d.date).utc().startOf("day").isSame(date.startOf("day"), "days")) {
        availableHours = allHours.filter(h => h == moment(d.date).utc().format("LT"))

For example, I have in this day 2 meetings planned at 16:00 and at 18:00.

On the first iteration, it has filtered the 16:00 like expected.

const availableHours = [
  "10:00",
  "11:00",
  "12:00",
  "13:00",
  "14:00",
  "15:00",
  -
  "17:00",
  "18:00",
  "19:00",
];

When it iterates a second time, its start from the beginning, and the available array returns the allHours array without 18:00, The final availableHours array I get is:

const allHours = [
  "10:00",
  "11:00",
  "12:00",
  "13:00",
  "14:00",
  "15:00",
  "16:00",
  "17:00",
  --
  "19:00",
];

Which is wrong. The result should look like this:

const allHours = [
  "10:00",
  "11:00",
  "12:00",
  "13:00",
  "14:00",
  "15:00",
  --
  "17:00",
  --
  "19:00",
];

How can I fix this?

DAVID _ · Accepted Answer · 2020-11-16 14:54:53Z

1

It easy to fix

First of all, initialize availableHours via allHours;

let availableHours=[...allHours];

then use an availableHours for filtering in meeting loop

availableHours = availableHours.filter(...)

answered Nov 16, 2020 at 14:54

DAVID _

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1 Comment

Roei Grinshpan Over a year ago

thanks a lot. its what i looking for. i hope that is right way to do this and not take to much performance

Momen Zalabany · Accepted Answer · 2020-11-16 14:58:02Z

you don't need all those loops, one good performant way to do what you need is use Set datatype and clear intersection;

example:

    const allHours = [
    "10:00",
    "11:00",
    "12:00",
    "13:00",
    "14:00",
    "15:00",
    "16:00",
    "17:00",
    "18:00",
    "19:00",
   ];
   const busyHours = new Set(["16:00","18:00"])
   let availableHours= allHours.filter(item=>busyHours.has(item)===false);
   console.log( availableHours );

or you can even use a lookup map;

example:

        const allHours = [
        "10:00",
        "11:00",
        "12:00",
        "13:00",
        "14:00",
        "15:00",
        "16:00",
        "17:00",
        "18:00",
        "19:00",
       ];
       const busyHours = ["16:00", "18:00"]
       // convert array to Object using reduce;
       // { "16:00": true, "18:00": true }
       const busyHoursMap = busyHours.reduce((carry,item)=>({[item]:true, ...carry}),{});
       let availableHours= allHours.filter(item=>busyHoursMap[item]!==true);
       console.log( availableHours );

finally, if your arrays are not too big, then you should not care much about performance, and a simple array filter will do:-

        const allHours = [
        "10:00",
        "11:00",
        "12:00",
        "13:00",
        "14:00",
        "15:00",
        "16:00",
        "17:00",
        "18:00",
        "19:00",
       ];
       const busyHours = ["16:00", "18:00"]
       let availableHours= allHours.filter(item=>busyHours.indexOf(item)>-1);
       console.log( availableHours );

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