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scala-breeze

How to slice on arbitrary indices with breeze?

In Python's numpy, I can do this:

>>> import numpy as np
>>> m = np.array([[1,2,3,4],[5,6,7,8],[9,10,11,12]])
>>> indices = [1,3]
>>> m[:,indices]
array([[ 2,  4],
       [ 6,  8],
       [10, 12]])

In other words, I can slice based on an arbitrary (not necessarily contiguous) list of indices. How can I do something similar in Breeze? I'm looking for something efficient and preferably elegant.

Solution

  • More or less identically to numpy: 

    scala> import breeze.linalg._
import breeze.linalg._

scala> val m = DenseMatrix((1,2,3,4),(5,6,7,8),(9,10,11,12))
m: breeze.linalg.DenseMatrix[Int] =
1  2   3   4
5  6   7   8
9  10  11  12

scala> val indices = IndexedSeq(1,3)
indices: IndexedSeq[Int] = Vector(1, 3)

scala> m(::, indices)
res0: breeze.linalg.SliceMatrix[Int,Int,Int] =
2   4
6   8
10  12