RE: [Numpy-discussion] Finding indices and setting values

[Perry G. <pe...@st...>]

>=20
> x,y =3D Numeric.indices((512,512))
> r =3D x**2 + y**2
> c =3D r < N=20
>=20
> In numarray you can then say:
>=20
> a[ c ] =3D 1
>=20
> In Numeric, I think you say:
>=20
> a =3D a.flat
> c =3D c.flat
> Numeric.put(a, Numeric.nonzero(c), 1)
> a.shape =3D (512,512)
>=20
>=20
> Todd
>=20
Yeah, that's what I would do in Numeric :-)

I was thinking that the solution I gave was wasteful of memory
if N was generally much smaller than the dimensions of data.
Something like this (also untested) would be better in that
regard (again for numarray)

y, x =3D indices((2*N+1, 2*N+1))
yind, xind =3D nonzero(((x-N)**2+(y-N)**2) < N**2)=20
data[yind+y0-N, xind+x0-N] =3D 1

Note that this doesn't check to see if x0 and y0 are at least
N away from the boundaries of data, and also note my convention
for x and y is different than what Todd used (it depends on how
you interpret data in arrays, the convention I use is more common
for image data if you think of x corresponding to the most rapidly
varying index). The advantage of this approach is that the x and y
arrays are small if N is small, and computing xind, yind take much
less time than for very large arrays.

Doing this with Numeric would be much messier I believe (but a clever
person could prove me wrong).

Perry Greenfield