Scala中的上三角矩阵

Question

有没有办法可以在scala中更快地计算上三角矩阵？

/** Returns a vector which consists of the upper triangular elements of a matrix */   
def getUpperTriangle(A: Array[Array[Double]]) = 
{
    var A_ = Seq(0.)
    for (i <- 0 to A.size - 1;j <- 0 to A(0).size - 1)
    {
        if (i <= j){
            A_ = A_ ++ Seq(A(i)(j))
            }
    }
    A_.tail.toArray
}

Answer 1

我不知道更快,但这更短,更"功能"(我注意到你标记了你的问题functional-programming)

def getUpperTriangle(a: Array[Array[Double]]) = 
   (0 until a.size).flatMap(i => a(i).drop(i)).toArray

或者,或多或少相同的想法:

def getUpperTriangle(a: Array[Array[Double]]) =
   a.zipWithIndex.flatMap{case(r,i) => r.drop(i)}