How to filter array in react native?

Question

I have array

 const arr = [
    {id: 1, country: 'Austria'},
    {id: 2, country: 'Germany'},
    {id: 3, country: 'Austria'},
  ];

I tried the following the code to filter it.

arry.map((item,idx) => (
   item.country== "Austria"?(
       console.log(item.id)
   )
   :
   null
))

The output is

1 3

, but I want to get output after whole filter like

1,3

I want only the IDs where country is Austria as given below.

1,3

Answer 1

use reduce function

const arry = [
    {id: 1, country: 'Austria'},
    {id: 2, country: 'Germany'},
    {id: 3, country: 'Austria'},
  ];
  
   const result = arry.reduce((acc,item,idx) => {
    
          if(item.country == "Austria"){
             if(idx === 0) acc += item.id
             else acc += `,${item.id}`
           }
           
           return acc
      
    }, '')
    
    console.log(result)