Scala!

val result = arr.groupBy(x => if (x > 0) 1 else (if (x<0) -1 else 0)).mapValues(y => y.size.toDouble / arr.size)

println(result.getOrElse( 1, 0)) // positive
println(result.getOrElse(-1, 0)) // negative
println(result.getOrElse( 0, 0)) // zeroes