JavaScript - Array mapping with another array

Question

I have two arrays which starts off as this:

let days = [null, null, null, null, null, null, null];

const weekdays = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday']

Depending on what data I'm given, I want to map a new array with the corresponding weekday, but still keep it the same size array.

let numDays = ["0","2","4"]

let days = days.map(?)

days
> ['Sunday', null, 'Tuesday', null, 'Thursday', null, null]

I have attempted a conversion function which can convert numDays to its correspondingweekdays

const convert = function (c) {
  return weekdays[c];
}

numDays.map(convert)
> ['Sunday', 'Tuesday', 'Thursday']

But not sure how to retain the array size for the result I need.

Cheers!

map returns an array with the same size of the array you are executing it on. you can not simply use map for that. — Aᴍɪʀ
– Aᴍɪʀ, Commented Dec 19, 2016 at 2:31
I'm executing map on days which will give me the correct array size (7 elements). My question is figuring out how to use numDays as a reference index to replace the weekdays in days. — Robert Hung
– Robert Hung, Commented Dec 19, 2016 at 2:34

kevguy · Accepted Answer · 2016-12-19 03:28:09Z

2

I don't think you need the days variable to be [null, null, null, null, null, null, null].

const weekdays = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];

let numDays = ["0","2","4"];

var days = weekdays.map(function(day, index){
  if (numDays.indexOf(index.toString()) >= 0){
    return day;
  } else {
    return null;
  }
});

console.log(days);

answered Dec 19, 2016 at 3:28

kevguy

4,4381 gold badge27 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

dtkaias · Accepted Answer · 2016-12-19 02:46:07Z

2

This approach might be easier than using map, you can use forEach to loop over the required indexes, look up the day and add them to your days array as required.

const weekdays = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday']
let numDays = ["0","2","4"]
let days = [null, null, null, null, null, null, null];
numDays.forEach(i=>days[i] = weekdays[i]);
console.log(days);

edited Dec 19, 2016 at 2:46

answered Dec 19, 2016 at 2:41

dtkaias

7814 silver badges14 bronze badges

2 Comments

Aᴍɪʀ Over a year ago

but you need to define an array with 7 null elements.

dtkaias Over a year ago

The question stated that the array of nulls was already defined, if a more general array of n nulls is needed you could use something like let days = Array(7).fill(null)

Collectives™ on Stack Overflow

JavaScript - Array mapping with another array

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest