RE: [Numpy-discussion] searchsorted

[Nadav H. <na...@vi...>]

-----Original Message-----
From:	Perry Greenfield [mailto:pe...@st...]
Sent:	Tue 01-Jun-04 19:16
To:	Nadav Horesh; numpy-discussion
Cc:=09
Subject:	RE: [Numpy-discussion] searchsorted
Nadav Horesh writes

> I am currently working on a simulation that makes a heavy use of=20
> searchsorted. But it does not precisely fit to what I need --- if a=20
> value v is between p and q  searchsorted returns the index of q, while =

> what I need is the index of p.
>=20
> Currently my solution is to turn to floating points numbers:
>=20
> =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>=20
> Python 2.3.4 (#1, May 31 2004, 09:13:03)
> [GCC 3.4.0] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
> from numarray import *
>=20
> bins =3D array((0,10,20,30))
> val =3D array((10, 15))
> searchsorted(bins, val)
> array([1, 2])  # I really would like to get array([1, 1])
>=20
> # Here is the trick:
>=20
> fb =3D bins - 0.1
> fb
> array([ -0.1,   9.9,  19.9,  29.9])
>=20
> searchsorted(fb, val) - 1
> array([1, 1])    #  That's  it!
>=20
This is only approximate, right? If val =3D array([9.95, 15])
you will get the wrong answer won't you?

> =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>=20
> My questions are:
>=20
>    1. Is there a more elegant solution?
>    2. I am thinking of letting "searchsorted" return a second boolean
>       array which has the value True for every exact match:
>        >>> searchsorted(bins, val)
>        >>> [array([1, 2]), array([1, 0], type=3DBool)]
>       Any comments?
>=20
> Nadav.
>=20
To get the latter, you could so something like

ind =3D searchsorted(bins, val)
neq_mask =3D bins[ind]-val
ind[neq_mask] -=3D 1. # well, you need to handle where ind =3D 0 and
                    #  is not equal as well

Would that suffice?

Perry


-------------------------------------
Got the idea, the line should be really:

ind =3D ind - (bins[ind] !=3D val)


You helped a lot.

 Thank you very much,
   Nadav.