[Numpy-discussion] Boolean indexing

Robert Kern robert.kern@gmail....
Tue Mar 8 11:01:46 CST 2011

On Tue, Mar 8, 2011 at 07:59, Sam Tygier
<Sam.Tygier@hep.manchester.ac.uk> wrote:
> Hi
> I am having an  issue with boolean slicing. it seems to work fine for
> reading a value, but I can use it to set a value:
> import numpy
> b =  numpy.array([[1,2],[3,4],[5,6],[7,8],[9,10]])
> m = numpy.array([0,1,0,0,0], dtype=bool)
> print b[m]
> print b[m][0,0]
> b[m][0,0] = -1
> print b[m][0,0]
> I think the boolean slicing is making a copy instead of a view. is there
> a way around this?

bm = b[m]
bm[0,0] = -1
b[m] = bm

Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco

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