根据 Scala 中的条件，从同一集合的元素创建 Map

Question

I have a Hashset of the following form, it might grow big:

var hs = HashSet(("fox", "name"),
    ("animal", "type"),
    ("gender", "type"),
    ("x", "test"),
    ("x", "nottest"),
    ("z", "test"),
    ("z", "nottest"))

What is the best way to have a Map from it with the following form:

HashMap (("x", "test")-> ("x", "nottest"),("z", "test") ->("z", "nottest"))

ie Mapping the tuples from the same set where they have the same first element and the second element is prefixed with "not".

Answer 1

You can create all possible pairs and filter out the ones, that are not present in the original set:

hs.map { case(k, v) => (k, v) -> (k, "not" + v) }
  .filter { case(pos, neg) => hs.contains(neg) }
  .toMap

Edit:

If the set grows really large, then we can easily change the ordering - first check and filter only pairs with negations, then map:

hs.filter { case(k, v) => hs((k, "not" + v)) }
  .map { case(k, v) => (k, v) -> (k, "not" + v) }
  .toMap