Selecting elements from an array based on another array values in JavaScript

Question

Sorry for this basic question... I am relatively new to JS.

I have two arrays and want to select values from one based on the values of the other.

For example, if I have

var student = [10, 11, 21, 30, 31, 14];
var class   = [1,   1,  2,  3,  3,  1];

How would I proceed (ideally with filter and/or map) to get the list of student numbers in class = 1, for example.

I know how I would do it with a for-loop and push() function, but I think there should be a more elegant/concise way to perform that task in a single line command with map, filter or other functions.

Thanks in advance for any help.

what would be the list of resulting student numbers in class = 1? perhaps demonstrate what you have tried with the for-loop and push approach? — woozyking
– woozyking, Commented Feb 21, 2021 at 21:02

CertainPerformance · Accepted Answer · 2021-02-21 21:02:56Z

2

Filtering the students by checking the index in the other array would be pretty simple:

var student = [10, 11, 21, 30, 31, 14];
var classes   = [1,   1,  2,  3,  3,  1];

console.log(
  student.filter((_, i) => classes[i] === 1)
);

Keep in mind you cannot use class as a variable name - it's reserved. Use something else.

answered Feb 21, 2021 at 21:02

CertainPerformance

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Comments

Majed Badawi · Accepted Answer · 2021-02-21 21:04:54Z

0

class is a reserved word in JavaScript. To achieve the expected output, you can use .filter to return elements where classes[index] have the value of 1:

const students = [10, 11, 21, 30, 31, 14]; 
const classes =  [1,  1,  2,  3,  3,  1];

const getStudentsInClassOne = (arr=[]) => {
  if(arr.length !== classes.length) return;
  return arr.filter((e,index) => classes[index]===1);
}

console.log( getStudentsInClassOne(students) );

answered Feb 21, 2021 at 21:04

Majed Badawi

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