is it possible in kotlin to retrieve a value previously calculated for sorting, so that I don’t have...

# getting-started

[Daniele B]

is it possible in kotlin to retrieve a value previously calculated for sorting, so that I don’t have to calculate it twice?

myList
.sortedBy { val calculatedField = it.fieldA / it.fieldB }
.mapIndexed { index, elem -> MyNewObject(
    _index = index+2, 
    _value = calculatedField,
    _fieldA = fieldA.toInt()
    _fieldB= fieldB.toInt()
  )
}

unfortunately this code doesn’t work: I can’t access calculatedField from inside the map function

[Devil Ster 1]

what if reorder chain? Add property to MyNewObject (calculatedField) and then sort by this property?

[phldavies]

Or map to Pair<MyObj, SortVal> then sort on it.second?

[nanodeath]

myList
  .asSequence()
  .map { SortableThing(it, calculatedField = it.fieldA / it.fieldB) }
  .sortedBy { it.calculatedField }
  .mapIndexed { /* etc */ }
  .toList()

[nanodeath]

Pair would also do it

[nanodeath]

myList
  .asSequence()
  .map { it to (it.fieldA / it.fieldB) }
  .sortedBy { (_, cf) -> cf }
  .mapIndexed { idx, (l, _) -> /* etc */ }
  .toList()

[Daniele B]

@nanodeath thanks!

[ephemient]

a.k.a. https://en.wikipedia.org/wiki/Schwartzian_transform

[Daniele B]

@ephemient very interesting. Thanks!