[英]port java lambda predicate to scala
Iterables.filter(tree
// do the first search using the bounds
.search(bounds),
// refine using the exact distance
entry -> {
Point p = entry.geometry();
Position position = Position.create(p.y(), p.x());
return from.getDistanceToKm(position) < distanceKm;
});
從Java到Scala? 我下面的方法失敗了:
import com.github.davidmoten.grumpy.core.Position
import com.github.davidmoten.rtree2.{Iterables, RTree}
import com.github.davidmoten.rtree2.geometry.{Geometries, Point}
val sydney = Geometries.point(151.2094, -33.86)
val canberra = Geometries.point(149.1244, -35.3075)
val brisbane = Geometries.point(153.0278, -27.4679)
val bungendore = Geometries.point(149.4500, -35.2500)
var tree = RTree.star.create[String, Point]
tree = tree.add("Sydney", sydney)
tree = tree.add("Brisbane", brisbane)
val distanceKm = 300
val list = Iterables.toList(search(tree, canberra, distanceKm))
def createBounds(from: Position, distanceKm: Double) = { // this calculates a pretty accurate bounding box. Depending on the
// performance you require you wouldn't have to be this accurate because
// accuracy is enforced later
val north = from.predict(distanceKm, 0)
val south = from.predict(distanceKm, 180)
val east = from.predict(distanceKm, 90)
val west = from.predict(distanceKm, 270)
Geometries.rectangle(west.getLon, south.getLat, east.getLon, north.getLat)
}
import com.github.davidmoten.grumpy.core.Position
import com.github.davidmoten.rtree2.RTree
def search[T](tree: RTree[String, Point], lonLat: Point, distanceKm: Double) = { // First we need to calculate an enclosing lat long rectangle for this
// distance then we refine on the exact distance
val from = Position.create(lonLat.y, lonLat.x)
val bounds = createBounds(from, distanceKm)
Iterables.filter(tree.search // do the first search using the bounds
(bounds), // refine using the exact distance
(entry) => {
def foo(entry) = {
val p = entry.geometry
val position = Position.create(p.y, p.x)
from.getDistanceToKm(position) < distanceKm
}
foo(entry)
})
}
因為entry
類型似乎定義不明確。
tree
類型為RTree[String, Point]
所以T=String
, S=Point
。 因此tree.search(bounds)
類型為Iterable[Entry[String, Point]]
。 因此, entry
類型為Entry[String, Point]
。
嘗試
(entry: Entry[String,Point]) => {
def foo(entry: Entry[String,Point]) = {
val p = entry.geometry
val position = Position.create(p.y, p.x)
from.getDistanceToKm(position) < distanceKm
}
foo(entry)
})
在Scala 2.13.0,rtree2 0.9-RC1,脾氣暴躁的核心0.2.4中進行了測試。
在2.11中,這應該僅僅是
import scala.compat.java8.FunctionConverters._
((entry: Entry[String,Point]) => {
def foo(entry: Entry[String,Point]) = {
val p = entry.geometry
val position = Position.create(p.y, p.x)
from.getDistanceToKm(position) < distanceKm
}
foo(entry)
}).asJava
libraryDependencies += "org.scala-lang.modules" %% "scala-java8-compat" % "0.9.0"
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