# Issue

*This Content is from Stack Overflow. Question asked by onwkbapzjamrhoescc *

I have a service that returns a list of users, for each of users I have to calculate and get some codes based on user id and then I need to remove the last code since it’s not valid (in all cases) and then find the final code by calling another function with the list of codes(numbers).

```
let finalCode: number;
this.usersService.getUsers().subscribe(users => {
let userCodes: number[] = [];
for (const user of users) {
const codes = calculateUserCodes(user.id); // this functions returns an array with numbers [5, 2, 1];
codes.splice(-1);
userCodes.push(...codes);
}
userCodes = userCodes.sort((a, b) => a-b); // it is an array e.g [2,3,1]
finalCode = compareAndFindFinalCode(userCodes);
});
```

I did this solution but not sure if it’s efficient in Angular. So instead of for loop I wanted to use map and simplify:

```
let finalCode: number;
this.usersService.getUsers().subscribe(users => {
let a = colors.map(color => {
const codes = calculateUserCodes(user.id);
codes.splice(-1);
return codes;
}).sort((a, b) => a-b);
}
finalCode = compareAndFindFinalCode(userCodes);
```

But this doesn’t return this error `The right-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type.`

because the map creates a list of arrays instead of one array. Can someone help me solve this, please?

# Solution

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