[Numpy-discussion] Learn about numpy

[Nadav Horesh]

What you do here is a convolution with 

0 1 0
1 1 1
0 1 0

kernel, and thresholding, you can use numpy.numarray.nd_image package:

import numpy.numarray.nd_image as NI
.
.
.
   ker = array([[0,1,0], [1,1,1],[0,1,0]])
   result = (NI.convolve(self.bufbw, ker) == 1).astype(uint8)

for nore general cases you can use the function generic_filter in the same package.

   Nadav.


-----הודעה מקורית-----
מאת: numpy-discussion-bounces at scipy.org בשם Folkert Boonstra
נשלח: א 04-מאי-08 12:52
אל: numpy-discussion at scipy.org
נושא: [Numpy-discussion] Learn about numpy
 
With a python background but new to numpy, I have the following.

Suppose I have a 2-D array and I want to apply a function to each element.
The function needs to access the direct neighbouring elements in order
to set a new value for the element. How would I do that in the most
efficient way with numpy?

Currently I have a uint8 array (self.bufbw) filled with 0 and 1 elements:

    def applyRule(self, rule):
       for xy in self.xydims:
          rule(xy)

    def rule(self, xy):
        x = xy[0]; y = xy[1]
        sum = self.bufbw[x-1:x+2, y-1:y+2].sum() \
            - self.bufbw[x-1,y-1] - self.bufbw[x+1,y-1] \
            - self.bufbw[x-1,y+1] - self.bufbw[x+1,y+1]
        if sum == 1:
            self.bufbw[x,y] = 1
        else:
            self.bufbw[x,y] = 0

I have looked at the documentation online but couldn't find another faster solution yet. 
Does anyone want to share some ideas on a faster solution with numpy?

Thanks,
Folkert





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