需要 scala breeze 矩阵切片和向量索引的解决方法

Question

由于方法 foo 中的奇怪行为，我无法编写像 bar 这样的方法，我需要：

import breeze.linalg.DenseMatrix
import breeze.linalg.DenseVector

class Test {

    val dim = 3
    val X:DenseMatrix[Double] = DenseMatrix.rand(dim,dim)
    val u:DenseVector[Double] = DenseVector.fill(dim){1.0}

    def foo:Unit = {

        val i=0;
        val row_i:DenseVector[Double] = X(i,::).t  // OK
        val s = u(i)+u(i)                          // OK

        val j:Integer = 0
        val row_j:DenseVector[Double] = X(j,::).t  // does not compile (A)
        val a = u(j)+u(j)                          // does not compile (B)
    }
    def bar(i:Integer):Double = u(i)+u(i)          // does not compile (C)
}

有解决办法吗？预先感谢所有回复。

编译错误：

(A) could not find implicit value for parameter canSlice: breeze.linalg.support.CanSlice2[breeze.linalg.DenseMatrix[Double],Integer,collection.immutable.::.type,Result] not enough arguments for method apply: (implicit canSlice: breeze.linalg.support.CanSlice2[breeze.linalg.DenseMatrix[Double],Integer,collection.immutable.::.type,Result])

Result in trait TensorLike. Unspecified value parameter canSlice.

(B), (C)

could not find implicit value for parameter canSlice: breeze.linalg.support.CanSlice[breeze.linalg.DenseVector[Double],Integer,Result] not enough arguments for method apply: (implicit canSlice: breeze.linalg.support.CanSlice[breeze.linalg.DenseVector[Double],Integer,Result])Result in trait TensorLike. Unspecified value parameter canSlice.

Answer 1

首先：将 Integer 转换为 Int 。这至少会解决第一个编译错误。更新您的代码后会编译

import breeze.linalg.DenseMatrix
import breeze.linalg.DenseVector
import breeze.linalg.DenseMatrix
import breeze.linalg.DenseVector

class Test {

    val dim = 3
    val X:DenseMatrix[Double] = DenseMatrix.rand(dim,dim)
    val u:DenseVector[Double] = DenseVector.fill(dim){1.0}

    def foo:Unit = {

        val i=0;
        val row_i:DenseVector[Double] = X(i,::).t  // OK
        val s = u(i)+u(i)                          // OK

        val j:Int = 0
        val row_j:DenseVector[Double] = X(j,::).t  // does not compile (A)
        val a = u(j)+u(j)                          // does not compile (B)
    }
    def bar(i:Int):Double = u(i)+u(i)          // does not compile (C)
}

来自回复：

// Exiting paste mode, now interpreting.

import breeze.linalg.DenseMatrix
import breeze.linalg.DenseVector
defined class Test

所以你的其他错误对我来说也消失了 (scala 2.11.8)。如果您还有其他问题，请告诉我。

需要 scala breeze 矩阵切片和向量索引的解决方法

Need workaround for scala breeze matrix slicing and vector indexing

scala

vector

matrix

breeze