filtering numeric arrays

Lukasz Pankowski lupan at zamek.gda.pl
Mon Mar 3 17:57:37 CET 2003


"Marie-Claude Savoie" <marie-claude.savoie at sympatico.ca> writes:

> Hi All,
>
> I have an 2D numeric array of x,y points eg [(1,3),(2,4),(5,6)] and I would
> like to remove all the points in the array that don't meet the min/max point
> criteria.  I will have several thousand points.  With lists I can do it like
>
> [(x,y) for x,y in seq if xMin < x <xMax and yMin< y <yMax]
>
> How do I get the same functionality and better speed using numeric.  I have
> tried a bunch of things using compress and take but I am running up against
> a brick wall.
>
> Any ideas?
>
> Thanks
>
> Gordon Williams
>
>
>

Tested only for your example array :-), but should work:

from Numeric import *

# [(x,y) for x,y in seq if xMin < x <xMax and yMin< y <yMax]

a = array([(1,3),(2,4),(5,6)])

def filter_range(a, xMin, xMax, yMin, yMax):
    cc = greater(a, [xMin, yMin])
    cond = logical_and(cc[:,0], cc[:,1])
    less(a, [xMax, yMax], cc)
    logical_and(cond, cc[:,0], cond)
    logical_and(cond, cc[:,1], cond)
    return compress(cond, a, 0)

print filter_range(a, 0, 3,  3, 10)
print filter_range(a, 0, 7,  3, 10)
print filter_range(a, 0, 3,  0, 10)


-- 

=*= Lukasz Pankowski =*=

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