Breeze - Boolean Matrix

[Wei]

Happy Holidays, everyone.

I have been using matlab for many years and is happy to find a good library like Breeze providing similar functionality in Scala/Java. Just one quick question about indexing:

Is it possible to index dense matrix with boolean vector or matrix (this is commonly used in matlab)? Also, is boolean matrix boxed in Breeze?

Thanks.

[David Hall]

Yes, you can index matrices and vectors with boolean tensors of the same type. The result is a "slicevector", which is probably not the best choice, but it is what it is.

Boolean matrices are currently boxed. 

scala> import breeze.linalg._

import breeze.linalg._

scala> val dm = DenseMatrix.rand(5, 5)

dm: breeze.linalg.DenseMatrix[Double] =

0.410491337822108    0.2312409497063863  0.10312792066860399  ... (5 total)

0.7890078434527261   0.9253947875291468  0.162569349496404    ...

0.24325903507125846  0.3187495767083455  0.21208038727461864  ...

0.2298254089467855   0.9683842795421511  0.099865086522966    ...

0.36268636924825404  0.9489842096973167  0.20128043935517237  ...

scala> dm(dm :> 0.5)

res2: breeze.linalg.SliceVector[(Int, Int),Double] = breeze.linalg.SliceVector@fea1c37b

scala> res2.toDenseVector

res3: breeze.linalg.DenseVector[Double] = DenseVector(0.799357260499427, 0.7890078434527261, 0.9253947875291468, 0.9357039251969395, 0.7484777558659128, 0.9683842795421511, 0.8659207280590215, 0.5086632429613545, 0.9489842096973167, 0.8484530630703433, 0.8750651441258643)

scala> dm(dm :> 0.5) := 1.0

res4: breeze.linalg.Vector[Double] = breeze.linalg.SliceVector@5b135003

scala> dm

res5: breeze.linalg.DenseMatrix[Double] =

0.410491337822108    0.2312409497063863  0.10312792066860399  ... (5 total)

1.0                  1.0                 0.162569349496404    ...

0.24325903507125846  0.3187495767083455  0.21208038727461864  ...

0.2298254089467855   1.0                 0.099865086522966    ...

0.36268636924825404  1.0                 0.20128043935517237  ...

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[Wei]

Thanks for the quick reply, David.

The Boolean indexing is awesome and I really like it. Since this kind of indexing could me used often (especially in x(x > 0) kind of scenario), could you please consider supporting Boolean as unboxed?

Thanks again for the excellent work in Breeze. I can definitely see more and more academic and industry use with the library.