Best way to do tryMax and tryMin in F#?

Question

Suppose I have a seq and I want to return the largest if there are any elements or None otherwise. F# does not appear to have this built-in.

Here is my attempt:

let tryMax xs = 
  if Seq.isEmpty xs
  then 
    None
  else 
    Seq.max xs |> Some

let tryMin xs = 
  if Seq.isEmpty xs
  then 
    None
  else 
    Seq.min xs |> Some

• Are there any problems with this approach?
• Is there a built-in solution for this?

Answer 1

FWIW, here's tryMinBy as well:

let tryMinBy projection (items : seq<_>) =
    use e = items.GetEnumerator()
    if e.MoveNext() then
        let mutable minItem = e.Current
        let mutable minValue = projection minItem
        while e.MoveNext() do
            let value = projection e.Current
            if value < minValue then
                minItem <- e.Current
                minValue <- value
        Some minItem
    else
        None

---

The full suite:

module Seq

let tryMinBy projection (items : seq<_>) =
  use e = items.GetEnumerator ()

  if e.MoveNext ()
  then
    let mutable minItem = e.Current
    let mutable minValue = projection minItem

    while e.MoveNext () do
      let value = projection e.Current

      if value < minValue
      then
        minItem <- e.Current
        minValue <- value

    Some minItem
  else
    None

let tryMaxBy projection (items : seq<_>) =
  use e = items.GetEnumerator ()

  if e.MoveNext ()
  then
    let mutable maxItem = e.Current
    let mutable maxValue = projection maxItem

    while e.MoveNext () do
      let value = projection e.Current

      if value > maxValue
      then
        maxItem <- e.Current
        maxValue <- value

    Some maxItem
  else
    None

let tryMin (items : seq<_>) =
  use e = items.GetEnumerator ()

  if e.MoveNext ()
  then
    let mutable minItem = e.Current

    while e.MoveNext () do
      if e.Current < minItem
      then
        minItem <- e.Current

    Some minItem
  else
    None

let tryMax (items : seq<_>) =
  use e = items.GetEnumerator ()

  if e.MoveNext ()
  then
    let mutable maxItem = e.Current

    while e.MoveNext () do
      if e.Current > maxItem
      then
        maxItem <- e.Current

    Some maxItem
  else
    None