Function or logic to sort an array of numbers.

There's no (supported) sort function that we can use outside of the example I'm going to show you (I say "unsupported" because there *is* a function that exists but is flagged by Appian as being unsupported). 

a!sortInfo() is a system type that holds the instructions for how a sort operation should be applied. You need to use this within a datasubset. Here's how:

a!localVariables(
  local!array: { 1, 4, 6, 8, 5, 3 },
  local!fieldArray: a!forEach(
    items: local!array,
    expression: a!map(id: fv!item)
  ),
  local!datasubset: fn!todatasubset(
    arrayToPage: local!fieldArray,
    pagingConfiguration: a!pagingInfo(
      startIndex: 1,
      batchSize: - 1,
      sort: a!sortInfo(field: "id", ascending: true)
    )
  ),
  local!datasubset.data.id
)

Yes it's ugly and long-winded but it does the job.

Take a look at 'Sort Utilities' plugin. 

An Alternative solution 

What is the difference?