需要针对Scala微风矩阵切片和矢量索引的解决方法

Question

Because of the odd behaviour in method foo I cannot write methods like bar, which I need:

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)
}

Is there a workaround? Thanks in advance for all replies.

Compilation errors:

(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

First off: convert your Integer to Int . That would take care of at least the first compilation error. Following update to your code does compile

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)
}

From the repl:

// Exiting paste mode, now interpreting.

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

So your other errors also disappear for me (scala 2.11.8). Let me know if you have further issues.