c.reynolds - 4 months ago 43

Javascript Question

I have searched on here and have not found a solution. Obviously I will be corrected if I am wrong. What I am trying to do is return values that do not have a duplicates in an array.

Examples:

`myArr = [2,1,2,3] // answer [1,3]`

`myArr = [3,1,2,2,3] // answer [1]`

I would post some code but I have not been able to figure this out myself and the only code examples I have found are for removing any duplicate values.

The possible solution above is to return no duplicates... I am trying to return values that are don't have duplicates.

Answer

One option is to use the optional second argument to indexOf to find duplicate indexes. Consider that for a given element `e`

and an index `i`

:

- if
`e`

is the first of two identical elements in the array,`indexOf(e)`

will return`i`

and`indexOf(e, i + 1)`

will return the index of the second element. - if
`e`

is the second of two identical elements in the array,`indexOf(e)`

will return the index of the first element, and`indexOf(e, i + 1)`

will return`-1`

- if
`e`

is a unique element,`indexOf(e)`

will return`i`

and`indexOf(e, i + 1)`

will return`-1`

.

Therefore:

```
myArr.filter(function (e, i, a) {
return a.indexOf(e) === i && a.indexOf(e, i + 1) === -1
});
```