Remove Strings, Keep Numbers In Array With JavaScript

Question

Other articles talk about removing strings from an array based on a search term.

But I'm trying to indentify which elements are strings and which elements are numbers in an array, and then remove all strings to return a new array.

function filter_list(l) {

  let newArray = []; 

  for (let i = 0; i < l.length; i ++) {

     if (i !== "^[a-zA-Z0-9_.-]*$") {
       newArray = newArray + i;
     }
  }

  return newArray;

}

This is returning 0123.

1. Why is it not returning an array?
2. Why is if (i !== "^[a-zA-Z0-9_.-]*$") not working? How else can I check for when an element is a string (something in quotes) within the array?

https://www.codewars.com/kata/list-filtering/train/javascript

Thanks

Answer 1

You can is typeof keyword. and filter(). I have tested the code its passing all tests in codewars.

Using ES6 Arrow Function

function filter_list(l) {
  return l.filter(x => typeof x === "number");
}
console.log(filter_list([1,2,'a','b']))

Without Arrow Function

function filter_list(l) {
  return l.filter(function(x){
      return typeof x === "number"
    });
}
console.log(filter_list([1,2,'a','b']))

Using Simple Loops

function filter_list(l) {
  let newArr = [];
  for(let i = 0;i<l.length;i++){
    if(typeof l[i] === "number") newArr.push(l[i]);
  }
  return newArr
}
console.log(filter_list([1,2,'a','b']))

Answer 2

Regex is not good way to parse such table. Try isNaN

console.log(
    [1,2,3,4,5, 'a', 'b', 1, 3].filter(item => !isNaN(item) ? item : '')
)

If you want less hacky way try

function filter_list(l) { 
// l is very bad name, because look similar to i

  let newArray = []; 

  for (let i = 0; i < l.length; i ++) {
      !isNaN(l[i]) ? newArray.push(l[i]) : ''
  }
  return newArray;
}

or even

  for (let i = 0; i < l.length; i ++) {
      !isNaN(l[i]) ? newArray[i] = l[i] : ''
  }

Hovewer, this task can be done with regexes, but I cannot recommend this solution.

[1,2,3,4,5, 'a', 'b', 1, 3].join(' ').replace(/\D/gm, '').split('')

Answer 3

var numberArray: any[];
numberArray.filter(Number)

Using this you can filter only numbers in an array and then can performe what you want.

Answer 4

function filter_list(l) {
  return l.filter(x => typeof x === "number");
}
console.log(filter_list([1,2,'a','b']))