How to find max's index in a Seq, List or Array in F#

Question

`Seq.max` finds the max number. I'd like to have something like `Seq.findIndex` `Seq.maxIndex` returns the index of the maximum element.

Accepted Answer

I believe you are looking for something like:

```
let maxIndex seq = 
    fst (Seq.maxBy snd (Seq.mapi (fun i x -> i, x) seq))
```

Note that giving this function an empty sequence will result in an ArgumentException.

(Alternatively, written in pipelining style:

```
let maxIndex seq =  
    seq
    |> Seq.mapi (fun i x -> i, x)
    |> Seq.maxBy snd 
    |> fst
```

)

Solution