Slicing and updating non-contiguous indices in a DenseVector in Breeze

Asked Feb 03 '15 at 11:08

Active Feb 03 '15 at 11:23

Viewed 138 times

I want to do something like the following.

Equivalent code in NumPy

a = np.zeros(5)
a[np.array([1, 2, 4])] += [1, 2, 3]
a
array([ 0.,  1.,  2.,  0.,  3.])

I tried the following but it does not work.

val v = DenseVector.zeros[Double](5)
v(1, 2, 4) :+= DenseVector(1, 2, 3)

<console>:18: error: could not find implicit value for parameter op:breeze.linalg.operators.OpAdd.InPlaceImpl2[breeze.linalg.Vector[Double],breeze.linalg.DenseVector[Int]]
              v(1, 2, 4) += DenseVector(1, 2, 3)

Any help would be appreciated

edited Feb 03 '15 at 11:23

asked Feb 03 '15 at 11:08

Manoj

Please do not just say "it does not work". What didn't work? Compiler error? Run time error? Wrong result? What happened? What were you expecting? – The Archetypal Paul Feb 03 '15 at 11:21
And you can't just literally translate from Python to Scala! Your scala code doesn't really make any sense... what are you trying to do? Set the elements with indices 1, 2, and 4 to the values 1, 2, 3? – The Archetypal Paul Feb 03 '15 at 11:23
I've edited it, The thing is doing a slice like `v(1, 2, 4)` gives me a SliceVector which I'm not sure how to manipulate. The documentation is really sparse. – Manoj Feb 03 '15 at 11:25
Yes that's what I want to do. Sorry I answered before you could edit your comment. – Manoj Feb 03 '15 at 11:27
Figured it out. But I'm not sure it's the best way. `val indices = Array(1, 2, 4) val val_ = (1, 2, 3) indices.map(i => v(i) += val_(i))` – Manoj Feb 03 '15 at 11:44
1

`(indices zip val_) map {case (i, x) => v(i) = x}` maybe? – The Archetypal Paul Feb 03 '15 at 12:05
Thanks this is cleaner. – Manoj Feb 03 '15 at 13:03
open a bug on breeze too, please. That should work. – dlwh Feb 12 '15 at 00:45
Oh, it works! It was because of the int + double datatype – Manoj Feb 12 '15 at 12:08

Slicing and updating non-contiguous indices in a DenseVector in Breeze

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