I have the following array
const arr = [
{ id: 1, token: "aAdsDDwEwe43svdwe2Xua" },
{ id: 2, token: undefined }
];
And I need to filter out undefined tokens, and ignore the id field.
Something like:
const arr = [
{ id: 1, token: "aAdsDDwEwe43svdwe2Xua" },
{ id: 2, token: undefined },
];
const result = arr
.filter(({ token }) => token !== undefined)
.map(({ token }) => token);
console.log(result);Is it possible to do it in O(n) ? I mean, without navigating through the list twice.
const result = arr.reduce((acc,curr) => {
return curr.token !==undefined ? [...acc,curr.token] : acc
},[])
Firstly it is O(n). Just because we run over a loop two times, it does not become O(n^2).
Additionally, if you simply use a for loop you will realise how simple it is:
const arr = [
{ id: 1, token: "aAdsDDwEwe43svdwe2Xua", extraField : "x" },
{ id: 2, token: undefined, extraField : "x" }
];
let ans = [];
for(let i = 0 ; i < arr.length; i++){
if(arr[i].token!== undefined){
let { id, ...newBody } = arr[i];
ans.push(newBody);
}
}
console.log(ans);Used spread operator (...), to remove a particular property (here id).
If you are looking for array methods, the above could also be achieved using a .forEach()